typecons.d

// Written in the D programming language.

/**
This module implements a variety of type constructors, i.e., templates
that allow construction of new, useful general-purpose types.

Source:    $(PHOBOSSRC std/_typecons.d)

Macros:

WIKI = Phobos/StdVariant

Synopsis:

----
// value tuples
alias Coord = Tuple!(float, "x", float, "y", float, "z");
Coord c;
c[1] = 1;       // access by index
c.z = 1;        // access by given name
alias DicEntry = Tuple!(string, string); // names can be omitted

// Rebindable references to const and immutable objects
void bar()
{
    const w1 = new Widget, w2 = new Widget;
    w1.foo();
    // w1 = w2 would not work; can't rebind const object
    auto r = Rebindable!(const Widget)(w1);
    // invoke method as if r were a Widget object
    r.foo();
    // rebind r to refer to another object
    r = w2;
}
----

Copyright: Copyright the respective authors, 2008-
License:   $(WEB boost.org/LICENSE_1_0.txt, Boost License 1.0).
Authors:   $(WEB erdani.org, Andrei Alexandrescu),
           $(WEB bartoszmilewski.wordpress.com, Bartosz Milewski),
           Don Clugston,
           Shin Fujishiro,
           Kenji Hara
 */
module std.typecons;
import std.traits, std.range;
import std.typetuple : TypeTuple, allSatisfy;

debug(Unique) import std.stdio;

/**
Encapsulates unique ownership of a resource.  Resource of type T is
deleted at the end of the scope, unless it is transferred.  The
transfer can be explicit, by calling $(D release), or implicit, when
returning Unique from a function. The resource can be a polymorphic
class object, in which case Unique behaves polymorphically too.

Example:
*/
struct Unique(T)
{
static if (is(T:Object))
    alias RefT = T;
else
    alias RefT = T*;

public:
/+ Doesn't work yet
    /**
    The safe constructor. It creates the resource and
    guarantees unique ownership of it (unless the constructor
    of $(D T) publishes aliases of $(D this)),
    */
    this(A...)(A args)
    {
        _p = new T(args);
    }
+/

    /**
    Constructor that takes an rvalue.
    It will ensure uniqueness, as long as the rvalue
    isn't just a view on an lvalue (e.g., a cast)
    Typical usage:
    ----
    Unique!(Foo) f = new Foo;
    ----
    */
    this(RefT p)
    {
        debug(Unique) writeln("Unique constructor with rvalue");
        _p = p;
    }
    /**
    Constructor that takes an lvalue. It nulls its source.
    The nulling will ensure uniqueness as long as there
    are no previous aliases to the source.
    */
    this(ref RefT p)
    {
        _p = p;
        debug(Unique) writeln("Unique constructor nulling source");
        p = null;
        assert(p is null);
    }
/+ Doesn't work yet
    /**
    Constructor that takes a Unique of a type that is convertible to our type:
    Disallow construction from lvalue (force the use of release on the source Unique)
    If the source is an rvalue, null its content, so the destrutctor doesn't delete it

    Typically used by the compiler to return $(D Unique) of derived type as $(D Unique)
    of base type.

    Example:
    ----
    Unique!(Base) create()
    {
        Unique!(Derived) d = new Derived;
        return d; // Implicit Derived->Base conversion
    }
    ----
    */
    this(U)(ref Unique!(U) u) = null;
    this(U)(Unique!(U) u)
    {
        _p = u._p;
        u._p = null;
    }
+/

    ~this()
    {
        debug(Unique) writeln("Unique destructor of ", (_p is null)? null: _p);
        delete _p;
        _p = null;
    }
    bool isEmpty() const
    {
        return _p is null;
    }
    /** Returns a unique rvalue. Nullifies the current contents */
    Unique release()
    {
        debug(Unique) writeln("Release");
        auto u = Unique(_p);
        assert(_p is null);
        debug(Unique) writeln("return from Release");
        return u;
    }
    /** Forwards member access to contents */
    RefT opDot() { return _p; }

/+ doesn't work yet!
    /**
    Postblit operator is undefined to prevent the cloning of $(D Unique) objects
    */
    this(this) = null;
 +/

private:
    RefT _p;
}

/+ doesn't work yet
unittest
{
    writeln("Unique class");
    class Bar
    {
        ~this() { writefln("    Bar destructor"); }
        int val() const { return 4; }
    }
    alias UBar = Unique!(Bar);
    UBar g(UBar u)
    {
        return u;
    }
    auto ub = UBar(new Bar);
    assert(!ub.isEmpty);
    assert(ub.val == 4);
    // should not compile
    // auto ub3 = g(ub);
    writeln("Calling g");
    auto ub2 = g(ub.release);
    assert(ub.isEmpty);
    assert(!ub2.isEmpty);
}

unittest
{
    writeln("Unique struct");
    struct Foo
    {
        ~this() { writefln("    Bar destructor"); }
        int val() const { return 3; }
    }
    alias UFoo = Unique!(Foo);

    UFoo f(UFoo u)
    {
        writeln("inside f");
        return u;
    }

    auto uf = UFoo(new Foo);
    assert(!uf.isEmpty);
    assert(uf.val == 3);
    // should not compile
    // auto uf3 = f(uf);
    writeln("Unique struct: calling f");
    auto uf2 = f(uf.release);
    assert(uf.isEmpty);
    assert(!uf2.isEmpty);
}
+/


/**
Tuple of values, for example $(D Tuple!(int, string)) is a record that
stores an $(D int) and a $(D string). $(D Tuple) can be used to bundle
values together, notably when returning multiple values from a
function. If $(D obj) is a tuple, the individual members are
accessible with the syntax $(D obj[0]) for the first field, $(D obj[1])
for the second, and so on.

The choice of zero-based indexing instead of one-base indexing was
motivated by the ability to use value tuples with various compile-time
loop constructs (e.g. type tuple iteration), all of which use
zero-based indexing.

Example:

----
Tuple!(int, int) point;
// assign coordinates
point[0] = 5;
point[1] = 6;
// read coordinates
auto x = point[0];
auto y = point[1];
----

Tuple members can be named. It is legal to mix named and unnamed
members. The method above is still applicable to all fields.

Example:

----
alias Entry = Tuple!(int, "index", string, "value");
Entry e;
e.index = 4;
e.value = "Hello";
assert(e[1] == "Hello");
assert(e[0] == 4);
----

Tuples with named fields are distinct types from tuples with unnamed
fields, i.e. each naming imparts a separate type for the tuple. Two
tuple differing in naming only are still distinct, even though they
might have the same structure.

Example:

----
Tuple!(int, "x", int, "y") point1;
Tuple!(int, int) point2;
assert(!is(typeof(point1) == typeof(point2))); // passes
----
*/
template Tuple(Specs...)
{
    import std.typetuple : staticMap;

    // Parse (type,name) pairs (FieldSpecs) out of the specified
    // arguments. Some fields would have name, others not.
    template parseSpecs(Specs...)
    {
        static if (Specs.length == 0)
        {
            alias parseSpecs = TypeTuple!();
        }
        else static if (is(Specs[0]))
        {
            static if (is(typeof(Specs[1]) : string))
            {
                alias parseSpecs =
                    TypeTuple!(FieldSpec!(Specs[0 .. 2]),
                               parseSpecs!(Specs[2 .. $]));
            }
            else
            {
                alias parseSpecs =
                    TypeTuple!(FieldSpec!(Specs[0]),
                               parseSpecs!(Specs[1 .. $]));
            }
        }
        else
        {
            static assert(0, "Attempted to instantiate Tuple with an "
                            ~"invalid argument: "~ Specs[0].stringof);
        }
    }

    template FieldSpec(T, string s = "")
    {
        alias Type = T;
        alias name = s;
    }

    alias fieldSpecs = parseSpecs!Specs;

    // Used with staticMap.
    alias extractType(alias spec) = spec.Type;
    alias extractName(alias spec) = spec.name;

    // Generates named fields as follows:
    //    alias name_0 = Identity!(field[0]);
    //    alias name_1 = Identity!(field[1]);
    //      :
    // NOTE: field[k] is an expression (which yields a symbol of a
    //       variable) and can't be aliased directly.
    string injectNamedFields()
    {
        string decl = "";
        foreach (i, name; staticMap!(extractName, fieldSpecs))
        {
            import std.string : format;

            decl ~= format("alias _%s = Identity!(field[%s]);", i, i);
            if (name.length != 0)
            {
                decl ~= format("alias %s = _%s;", name, i);
            }
        }
        return decl;
    }

    // Returns Specs for a subtuple this[from .. to] preserving field
    // names if any.
    alias sliceSpecs(size_t from, size_t to) =
        staticMap!(expandSpec, fieldSpecs[from .. to]);

    template expandSpec(alias spec)
    {
        static if (spec.name.length == 0)
        {
            alias expandSpec = TypeTuple!(spec.Type);
        }
        else
        {
            alias expandSpec = TypeTuple!(spec.Type, spec.name);
        }
    }

    enum areCompatibleTuples(Tup1, Tup2, string op) = isTuple!Tup2 && is(typeof(
    {
        Tup1 tup1 = void;
        Tup2 tup2 = void;
        static assert(tup1.field.length == tup2.field.length);
        foreach (i, _; Tup1.Types)
        {
            auto lhs = typeof(tup1.field[i]).init;
            auto rhs = typeof(tup2.field[i]).init;
            auto result = mixin("lhs "~op~" rhs");
        }
    }));

    enum areBuildCompatibleTuples(Tup1, Tup2) = isTuple!Tup2 && is(typeof(
    {
        static assert(Tup1.Types.length == Tup2.Types.length);
        foreach (i, _; Tup1.Types)
            static assert(isBuildable!(Tup1.Types[i], Tup2.Types[i]));
    }));

    /+ Returns $(D true) iff a $(D T) can be initialized from a $(D U). +/
    enum isBuildable(T, U) =  is(typeof(
    {
        U u = U.init;
        T t = u;
    }));
    /+ Helper for partial instanciation +/
    template isBuildableFrom(U)
    {
        enum isBuildableFrom(T) = isBuildable!(T, U);
    }

    struct Tuple
    {
        /**
         * The type of the tuple's components.
         */
        alias Types = staticMap!(extractType, fieldSpecs);

        /**
         * Use $(D t.expand) for a tuple $(D t) to expand it into its
         * components. The result of $(D expand) acts as if the tuple components
         * were listed as a list of values. (Ordinarily, a $(D Tuple) acts as a
         * single value.)
         *
         * Examples:
         * ----
         * auto t = tuple(1, " hello ", 2.3);
         * writeln(t);        // Tuple!(int, string, double)(1, " hello ", 2.3)
         * writeln(t.expand); // 1 hello 2.3
         * ----
         */
        Types expand;
        mixin(injectNamedFields());

        static if (is(Specs))
        {
            // This is mostly to make t[n] work.
            alias expand this;
        }
        else
        {
            @property
            ref inout(Tuple!Types) _Tuple_super() inout @trusted
            {
                foreach (i, _; Types)   // Rely on the field layout
                {
                    static assert(typeof(return).init.tupleof[i].offsetof ==
                                                       expand[i].offsetof);
                }
                return *cast(typeof(return)*) &(field[0]);
            }
            // This is mostly to make t[n] work.
            alias _Tuple_super this;
        }

        // backwards compatibility
        alias field = expand;

        /**
         * Constructor taking one value for each field.
         */
        this(Types values)
        {
            field[] = values[];
        }

        /**
         * Constructor taking a compatible array.
         *
         * Examples:
         * ----
         * int[2] ints;
         * Tuple!(int, int) t = ints;
         * ----
         */
        this(U, size_t n)(U[n] values)
        if (n == Types.length && allSatisfy!(isBuildableFrom!U, Types))
        {
            foreach (i, _; Types)
            {
                field[i] = values[i];
            }
        }

        /**
         * Constructor taking a compatible tuple.
         */
        this(U)(U another)
        if (areBuildCompatibleTuples!(typeof(this), U))
        {
            field[] = another.field[];
        }

        /**
         * Comparison for equality.
         */
        bool opEquals(R)(R rhs)
        if (areCompatibleTuples!(typeof(this), R, "=="))
        {
            return field[] == rhs.field[];
        }
        /// ditto
        bool opEquals(R)(R rhs) const
        if (areCompatibleTuples!(typeof(this), R, "=="))
        {
            return field[] == rhs.field[];
        }

        /**
         * Comparison for ordering.
         */
        int opCmp(R)(R rhs)
        if (areCompatibleTuples!(typeof(this), R, "<"))
        {
            foreach (i, Unused; Types)
            {
                if (field[i] != rhs.field[i])
                {
                    return field[i] < rhs.field[i] ? -1 : 1;
                }
            }
            return 0;
        }
        /// ditto
        int opCmp(R)(R rhs) const
        if (areCompatibleTuples!(typeof(this), R, "<"))
        {
            foreach (i, Unused; Types)
            {
                if (field[i] != rhs.field[i])
                {
                    return field[i] < rhs.field[i] ? -1 : 1;
                }
            }
            return 0;
        }

        /**
         * Assignment from another tuple. Each element of the source must be
         * implicitly assignable to the respective element of the target.
         */
        void opAssign(R)(auto ref R rhs)
        if (areCompatibleTuples!(typeof(this), R, "="))
        {
            import std.algorithm : swap;

            static if (is(R : Tuple!Types) && !__traits(isRef, rhs))
            {
                if (__ctfe)
                {
                    // Cannot use swap at compile time
                    field[] = rhs.field[];
                }
                else
                {
                    // Use swap-and-destroy to optimize rvalue assignment
                    swap!(Tuple!Types)(this, rhs);
                }
            }
            else
            {
                // Do not swap; opAssign should be called on the fields.
                field[] = rhs.field[];
            }
        }

        /**
         * Takes a slice of the tuple.
         *
         * Examples:
         * ----
         * Tuple!(int, string, float, double) a;
         * a[1] = "abc";
         * a[2] = 4.5;
         * auto s = a.slice!(1, 3);
         * static assert(is(typeof(s) == Tuple!(string, float)));
         * assert(s[0] == "abc" && s[1] == 4.5);
         * ----
         */
        @property
        ref Tuple!(sliceSpecs!(from, to)) slice(size_t from, size_t to)() @trusted
        if (from <= to && to <= Types.length)
        {
            return *cast(typeof(return)*) &(field[from]);
        }

        /**
         * Converts to string.
         */
        static if (allSatisfy!(isPrintable, Types))
        string toString()
        {
            enum header = typeof(this).stringof ~ "(",
                 footer = ")",
                 separator = ", ";

            Appender!string w;
            w.put(header);
            foreach (i, Unused; Types)
            {
                static if (i > 0)
                {
                    w.put(separator);
                }
                // TODO: Change this once toString() works for shared objects.
                static if (is(Unused == class) && is(Unused == shared))
                    formattedWrite(w, "%s", field[i].stringof);
                else
                {
                    import std.format : FormatSpec, formatElement;

                    FormatSpec!char f;  // "%s"
                    formatElement(w, field[i], f);
                }
            }
            w.put(footer);
            return w.data;
        }
    }
}

private enum bool isPrintable(T) =
    is(typeof({
        import std.format : formattedWrite;

        Appender!string w;
        formattedWrite(w, "%s", T.init);
    }));

private alias Identity(alias T) = T;

/**
    Return a copy of a Tuple with its fields in reverse order.
 */
ReverseTupleType!T reverse(T)(T t)
    if (isTuple!T)
{
    import std.typetuple : Reverse;
    // @@@BUG@@@ Cannot be an internal function due to forward reference issues.

    // @@@BUG@@@ 9929 Need 'this' when calling template with expanded tuple
    // return tuple(Reverse!(t.expand));

    typeof(return) result;
    auto tup = t.expand;
    result.expand = Reverse!tup;
    return result;
}

///
unittest
{
    auto tup = tuple(1, "2");
    assert(tup.reverse == tuple("2", 1));
}

/* Get a Tuple type with the reverse specification of Tuple T. */
private template ReverseTupleType(T)
    if (isTuple!T)
{
    static if (is(T : Tuple!A, A...))
        alias ReverseTupleType = Tuple!(ReverseTupleSpecs!A);
}

/* Reverse the Specs of a Tuple. */
private template ReverseTupleSpecs(T...)
{
    static if (T.length > 1)
    {
        static if (is(typeof(T[$-1]) : string))
        {
            alias ReverseTupleSpecs = TypeTuple!(T[$-2], T[$-1], ReverseTupleSpecs!(T[0 .. $-2]));
        }
        else
        {
            alias ReverseTupleSpecs = TypeTuple!(T[$-1], ReverseTupleSpecs!(T[0 .. $-1]));
        }
    }
    else
    {
        alias ReverseTupleSpecs = T;
    }
}

unittest
{
    {
        Tuple!(int, "a", int, "b") nosh;
        static assert(nosh.length == 2);
        nosh.a = 5;
        nosh.b = 6;
        assert(nosh.a == 5);
        assert(nosh.b == 6);
    }
    {
        Tuple!(short, double) b;
        static assert(b.length == 2);
        b[1] = 5;
        auto a = Tuple!(int, real)(b);
        assert(a[0] == 0 && a[1] == 5);
        a = Tuple!(int, real)(1, 2);
        assert(a[0] == 1 && a[1] == 2);
        auto c = Tuple!(int, "a", double, "b")(a);
        assert(c[0] == 1 && c[1] == 2);
    }
    {
        Tuple!(int, real) nosh;
        nosh[0] = 5;
        nosh[1] = 0;
        assert(nosh[0] == 5 && nosh[1] == 0);
        assert(nosh.toString() == "Tuple!(int, real)(5, 0)", nosh.toString());
        Tuple!(int, int) yessh;
        nosh = yessh;
    }
    {
        Tuple!(int, string) t;
        t[0] = 10;
        t[1] = "str";
        assert(t[0] == 10 && t[1] == "str");
        assert(t.toString() == `Tuple!(int, string)(10, "str")`, t.toString());
    }
    {
        Tuple!(int, "a", double, "b") x;
        static assert(x.a.offsetof == x[0].offsetof);
        static assert(x.b.offsetof == x[1].offsetof);
        x.b = 4.5;
        x.a = 5;
        assert(x[0] == 5 && x[1] == 4.5);
        assert(x.a == 5 && x.b == 4.5);
    }
    // indexing
    {
        Tuple!(int, real) t;
        static assert(is(typeof(t[0]) == int));
        static assert(is(typeof(t[1]) == real));
        int* p0 = &t[0];
        real* p1 = &t[1];
        t[0] = 10;
        t[1] = -200.0L;
        assert(*p0 == t[0]);
        assert(*p1 == t[1]);
    }
    // slicing
    {
        Tuple!(int, "x", real, "y", double, "z", string) t;
        t[0] = 10;
        t[1] = 11;
        t[2] = 12;
        t[3] = "abc";
        auto a = t.slice!(0, 3);
        assert(a.length == 3);
        assert(a.x == t.x);
        assert(a.y == t.y);
        assert(a.z == t.z);
        auto b = t.slice!(2, 4);
        assert(b.length == 2);
        assert(b.z == t.z);
        assert(b[1] == t[3]);
    }
    // nesting
    {
        Tuple!(Tuple!(int, real), Tuple!(string, "s")) t;
        static assert(is(typeof(t[0]) == Tuple!(int, real)));
        static assert(is(typeof(t[1]) == Tuple!(string, "s")));
        static assert(is(typeof(t[0][0]) == int));
        static assert(is(typeof(t[0][1]) == real));
        static assert(is(typeof(t[1].s) == string));
        t[0] = tuple(10, 20.0L);
        t[1].s = "abc";
        assert(t[0][0] == 10);
        assert(t[0][1] == 20.0L);
        assert(t[1].s == "abc");
    }
    // non-POD
    {
        static struct S
        {
            int count;
            this(this) { ++count; }
            ~this() { --count; }
            void opAssign(S rhs) { count = rhs.count; }
        }
        Tuple!(S, S) ss;
        Tuple!(S, S) ssCopy = ss;
        assert(ssCopy[0].count == 1);
        assert(ssCopy[1].count == 1);
        ssCopy[1] = ssCopy[0];
        assert(ssCopy[1].count == 2);
    }
    // bug 2800
    {
        static struct R
        {
            Tuple!(int, int) _front;
            @property ref Tuple!(int, int) front() { return _front;  }
            @property bool empty() { return _front[0] >= 10; }
            void popFront() { ++_front[0]; }
        }
        foreach (a; R())
        {
            static assert(is(typeof(a) == Tuple!(int, int)));
            assert(0 <= a[0] && a[0] < 10);
            assert(a[1] == 0);
        }
    }
    // Construction with compatible elements
    {
        auto t1 = Tuple!(int, double)(1, 1);

        // 8702
        auto t8702a = tuple(tuple(1));
        auto t8702b = Tuple!(Tuple!(int))(Tuple!(int)(1));
    }
    // Construction with compatible tuple
    {
        Tuple!(int, int) x;
        x[0] = 10;
        x[1] = 20;
        Tuple!(int, "a", double, "b") y = x;
        assert(y.a == 10);
        assert(y.b == 20);
        // incompatible
        static assert(!__traits(compiles, Tuple!(int, int)(y)));
    }
    // 6275
    {
        const int x = 1;
        auto t1 = tuple(x);
        alias T = Tuple!(const(int));
        auto t2 = T(1);
    }
    // 9431
    {
        alias T = Tuple!(int[1][]);
        auto t = T([[10]]);
    }
    // 7666
    {
        auto tup = tuple(1, "2");
        assert(tup.reverse == tuple("2", 1));
    }
    {
        Tuple!(int, "x", string, "y") tup = tuple(1, "2");
        auto rev = tup.reverse;
        assert(rev == tuple("2", 1));
        assert(rev.x == 1 && rev.y == "2");
    }
    {
        Tuple!(wchar, dchar, int, "x", string, "y", char, byte, float) tup;
        tup = tuple('a', 'b', 3, "4", 'c', cast(byte)0x0D, 0.00);
        auto rev = tup.reverse;
        assert(rev == tuple(0.00, cast(byte)0x0D, 'c', "4", 3, 'b', 'a'));
        assert(rev.x == 3 && rev.y == "4");
    }
}
unittest
{
    // opEquals
    {
        struct Equ1 { bool opEquals(Equ1) { return true; } }
        auto  tm1 = tuple(Equ1.init);
        const tc1 = tuple(Equ1.init);
        static assert( is(typeof(tm1 == tm1)));
        static assert(!is(typeof(tm1 == tc1)));
        static assert(!is(typeof(tc1 == tm1)));
        static assert(!is(typeof(tc1 == tc1)));

        struct Equ2 { bool opEquals(const Equ2) const { return true; } }
        auto  tm2 = tuple(Equ2.init);
        const tc2 = tuple(Equ2.init);
        static assert( is(typeof(tm2 == tm2)));
        static assert( is(typeof(tm2 == tc2)));
        static assert( is(typeof(tc2 == tm2)));
        static assert( is(typeof(tc2 == tc2)));

        struct Equ3 { bool opEquals(T)(T) { return true; } }
        auto  tm3 = tuple(Equ3.init);           // bugzilla 8686
        const tc3 = tuple(Equ3.init);
        static assert( is(typeof(tm3 == tm3)));
        static assert( is(typeof(tm3 == tc3)));
        static assert(!is(typeof(tc3 == tm3)));
        static assert(!is(typeof(tc3 == tc3)));

        struct Equ4 { bool opEquals(T)(T) const { return true; } }
        auto  tm4 = tuple(Equ4.init);
        const tc4 = tuple(Equ4.init);
        static assert( is(typeof(tm4 == tm4)));
        static assert( is(typeof(tm4 == tc4)));
        static assert( is(typeof(tc4 == tm4)));
        static assert( is(typeof(tc4 == tc4)));
    }
    // opCmp
    {
        struct Cmp1 { int opCmp(Cmp1) { return 0; } }
        auto  tm1 = tuple(Cmp1.init);
        const tc1 = tuple(Cmp1.init);
        static assert( is(typeof(tm1 < tm1)));
        static assert(!is(typeof(tm1 < tc1)));
        static assert(!is(typeof(tc1 < tm1)));
        static assert(!is(typeof(tc1 < tc1)));

        struct Cmp2 { int opCmp(const Cmp2) const { return 0; } }
        auto  tm2 = tuple(Cmp2.init);
        const tc2 = tuple(Cmp2.init);
        static assert( is(typeof(tm2 < tm2)));
        static assert( is(typeof(tm2 < tc2)));
        static assert( is(typeof(tc2 < tm2)));
        static assert( is(typeof(tc2 < tc2)));

        struct Cmp3 { int opCmp(T)(T) { return 0; } }
        auto  tm3 = tuple(Cmp3.init);
        const tc3 = tuple(Cmp3.init);
        static assert( is(typeof(tm3 < tm3)));
        static assert( is(typeof(tm3 < tc3)));
        static assert(!is(typeof(tc3 < tm3)));
        static assert(!is(typeof(tc3 < tc3)));

        struct Cmp4 { int opCmp(T)(T) const { return 0; } }
        auto  tm4 = tuple(Cmp4.init);
        const tc4 = tuple(Cmp4.init);
        static assert( is(typeof(tm4 < tm4)));
        static assert( is(typeof(tm4 < tc4)));
        static assert( is(typeof(tc4 < tm4)));
        static assert( is(typeof(tc4 < tc4)));
    }
    {
        int[2] ints = [ 1, 2 ];
        Tuple!(int, int) t = ints;
        assert(t[0] == 1 && t[1] == 2);
        Tuple!(long, uint) t2 = ints;
        assert(t2[0] == 1 && t2[1] == 2);
    }
}
@safe unittest
{
    auto t1 = Tuple!(int, "x", string, "y")(1, "a");
    assert(t1.x == 1);
    assert(t1.y == "a");
    void foo(Tuple!(int, string) t2) {}
    foo(t1);

    Tuple!(int, int)[] arr;
    arr ~= tuple(10, 20); // OK
    arr ~= Tuple!(int, "x", int, "y")(10, 20); // NG -> OK

    static assert(is(typeof(Tuple!(int, "x", string, "y").tupleof) ==
                     typeof(Tuple!(int,      string     ).tupleof)));
}
unittest
{
    // Bugzilla 10686
    immutable Tuple!(int) t1;
    auto r1 = t1[0]; // OK
    immutable Tuple!(int, "x") t2;
    auto r2 = t2[0]; // error
}
unittest
{
    import std.exception : assertCTFEable;

    // Bugzilla 10218
    assertCTFEable!(
    {
        auto t = tuple(1);
        t = tuple(2);   // assignment
    });
}
unittest
{
    class Foo{}
    Tuple!(immutable(Foo)[]) a;
}

unittest
{
    //Test non-assignable
    static struct S
    {
        int* p;
    }
    alias IS = immutable S;
    static assert(!isAssignable!IS);

    auto s = IS.init;

    alias TIS = Tuple!IS;
    TIS a = tuple(s);
    TIS b = a;

    alias TISIS = Tuple!(IS, IS);
    TISIS d = tuple(s, s);
    IS[2] ss;
    TISIS e = TISIS(ss);
}

/**
Returns a $(D Tuple) object instantiated and initialized according to
the arguments.

Example:
----
auto value = tuple(5, 6.7, "hello");
assert(value[0] == 5);
assert(value[1] == 6.7);
assert(value[2] == "hello");
----
*/

Tuple!T tuple(T...)(T args)
{
    return typeof(return)(args);
}

/**
Returns $(D true) if and only if $(D T) is an instance of the
$(D Tuple) struct template.
 */
template isTuple(T)
{
    static if (is(Unqual!T Unused : Tuple!Specs, Specs...))
    {
        enum isTuple = true;
    }
    else
    {
        enum isTuple = false;
    }
}

unittest
{
    static assert(isTuple!(Tuple!()));
    static assert(isTuple!(Tuple!(int)));
    static assert(isTuple!(Tuple!(int, real, string)));
    static assert(isTuple!(Tuple!(int, "x", real, "y")));
    static assert(isTuple!(Tuple!(int, Tuple!(real), string)));

    static assert(isTuple!(const Tuple!(int)));
    static assert(isTuple!(immutable Tuple!(int)));

    static assert(!isTuple!(int));
    static assert(!isTuple!(const int));

    struct S {}
    static assert(!isTuple!(S));
}


/**
$(D Rebindable!(T)) is a simple, efficient wrapper that behaves just
like an object of type $(D T), except that you can reassign it to
refer to another object. For completeness, $(D Rebindable!(T)) aliases
itself away to $(D T) if $(D T) is a non-const object type. However,
$(D Rebindable!(T)) does not compile if $(D T) is a non-class type.

Regular $(D const) object references cannot be reassigned:

----
class Widget { int x; int y() const { return x; } }
const a = new Widget;
a.y();          // fine
a.x = 5;        // error! can't modify const a
a = new Widget; // error! can't modify const a
----

However, $(D Rebindable!(Widget)) does allow reassignment, while
otherwise behaving exactly like a $(D const Widget):

----
auto a = Rebindable!(const Widget)(new Widget);
a.y();          // fine
a.x = 5;        // error! can't modify const a
a = new Widget; // fine
----

You may want to use $(D Rebindable) when you want to have mutable
storage referring to $(D const) objects, for example an array of
references that must be sorted in place. $(D Rebindable) does not
break the soundness of D's type system and does not incur any of the
risks usually associated with $(D cast).

 */
template Rebindable(T) if (is(T == class) || is(T == interface) || isDynamicArray!T)
{
    static if (!is(T X == const U, U) && !is(T X == immutable U, U))
    {
        alias Rebindable = T;
    }
    else static if (isDynamicArray!T)
    {
        alias Rebindable = const(ElementEncodingType!T)[];
    }
    else
    {
        struct Rebindable
        {
            private union
            {
                T original;
                U stripped;
            }
            void opAssign(T another) pure nothrow
            {
                stripped = cast(U) another;
            }
            void opAssign(Rebindable another) pure nothrow
            {
                stripped = another.stripped;
            }
            static if (is(T == const U))
            {
                // safely assign immutable to const
                void opAssign(Rebindable!(immutable U) another) pure nothrow
                {
                    stripped = another.stripped;
                }
            }

            this(T initializer) pure nothrow
            {
                opAssign(initializer);
            }

            @property ref inout(T) get() inout pure nothrow
            {
                return original;
            }

            alias get this;
        }
    }
}

/**
Convenience function for creating a $(D Rebindable) using automatic type
inference.
*/
Rebindable!T rebindable(T)(T obj)
if (is(T == class) || is(T == interface) || isDynamicArray!T)
{
    typeof(return) ret;
    ret = obj;
    return ret;
}

/**
This function simply returns the $(D Rebindable) object passed in.  It's useful
in generic programming cases when a given object may be either a regular
$(D class) or a $(D Rebindable).
*/
Rebindable!T rebindable(T)(Rebindable!T obj)
{
    return obj;
}

unittest
{
    interface CI { const int foo(); }
    class C : CI {
      int foo() const { return 42; }
      @property int bar() const { return 23; }
    }
    Rebindable!(C) obj0;
    static assert(is(typeof(obj0) == C));

    Rebindable!(const(C)) obj1;
    static assert(is(typeof(obj1.get) == const(C)), typeof(obj1.get).stringof);
    static assert(is(typeof(obj1.stripped) == C));
    obj1 = new C;
    assert(obj1.get !is null);
    obj1 = new const(C);
    assert(obj1.get !is null);

    Rebindable!(immutable(C)) obj2;
    static assert(is(typeof(obj2.get) == immutable(C)));
    static assert(is(typeof(obj2.stripped) == C));
    obj2 = new immutable(C);
    assert(obj1.get !is null);

    // test opDot
    assert(obj2.foo() == 42);
    assert(obj2.bar == 23);

    interface I { final int foo() const { return 42; } }
    Rebindable!(I) obj3;
    static assert(is(typeof(obj3) == I));

    Rebindable!(const I) obj4;
    static assert(is(typeof(obj4.get) == const I));
    static assert(is(typeof(obj4.stripped) == I));
    static assert(is(typeof(obj4.foo()) == int));
    obj4 = new class I {};

    Rebindable!(immutable C) obj5i;
    Rebindable!(const C) obj5c;
    obj5c = obj5c;
    obj5c = obj5i;
    obj5i = obj5i;
    static assert(!__traits(compiles, obj5i = obj5c));

    // Test the convenience functions.
    auto obj5convenience = rebindable(obj5i);
    assert(obj5convenience is obj5i);

    auto obj6 = rebindable(new immutable(C));
    static assert(is(typeof(obj6) == Rebindable!(immutable C)));
    assert(obj6.foo() == 42);

    auto obj7 = rebindable(new C);
    CI interface1 = obj7;
    auto interfaceRebind1 = rebindable(interface1);
    assert(interfaceRebind1.foo() == 42);

    const interface2 = interface1;
    auto interfaceRebind2 = rebindable(interface2);
    assert(interfaceRebind2.foo() == 42);

    auto arr = [1,2,3,4,5];
    const arrConst = arr;
    assert(rebindable(arr) == arr);
    assert(rebindable(arrConst) == arr);

    // Issue 7654
    immutable(char[]) s7654;
    Rebindable!(typeof(s7654)) r7654 = s7654;

    foreach (T; TypeTuple!(char, wchar, char, int))
    {
        static assert(is(Rebindable!(immutable(T[])) == immutable(T)[]));
        static assert(is(Rebindable!(const(T[])) == const(T)[]));
        static assert(is(Rebindable!(T[]) == T[]));
    }

    // Issue 12046
    static assert(!__traits(compiles, Rebindable!(int[1])));
    static assert(!__traits(compiles, Rebindable!(const int[1])));
}

/**
  Order the provided members to minimize size while preserving alignment.
  Returns a declaration to be mixed in.

Example:
---
struct Banner {
  mixin(alignForSize!(byte[6], double)(["name", "height"]));
}
---

  Alignment is not always optimal for 80-bit reals, nor for structs declared
  as align(1).
*/
string alignForSize(E...)(string[] names...)
{
    // Sort all of the members by .alignof.
    // BUG: Alignment is not always optimal for align(1) structs
    // or 80-bit reals or 64-bit primitives on x86.
    // TRICK: Use the fact that .alignof is always a power of 2,
    // and maximum 16 on extant systems. Thus, we can perform
    // a very limited radix sort.
    // Contains the members with .alignof = 64,32,16,8,4,2,1

    assert(E.length == names.length,
        "alignForSize: There should be as many member names as the types");

    string[7] declaration = ["", "", "", "", "", "", ""];

    foreach (i, T; E)
    {
        auto a = T.alignof;
        auto k = a>=64? 0 : a>=32? 1 : a>=16? 2 : a>=8? 3 : a>=4? 4 : a>=2? 5 : 6;
        declaration[k] ~= T.stringof ~ " " ~ names[i] ~ ";\n";
    }

    auto s = "";
    foreach (decl; declaration)
        s ~= decl;
    return s;
}

unittest
{
    enum x = alignForSize!(int[], char[3], short, double[5])("x", "y","z", "w");
    struct Foo { int x; }
    enum y = alignForSize!(ubyte, Foo, cdouble)("x", "y", "z");

    enum passNormalX = x == "double[5] w;\nint[] x;\nshort z;\nchar[3] y;\n";
    enum passNormalY = y == "cdouble z;\nFoo y;\nubyte x;\n";

    enum passAbnormalX = x == "int[] x;\ndouble[5] w;\nshort z;\nchar[3] y;\n";
    enum passAbnormalY = y == "Foo y;\ncdouble z;\nubyte x;\n";
    // ^ blame http://d.puremagic.com/issues/show_bug.cgi?id=231

    static assert(passNormalX || passAbnormalX && double.alignof <= (int[]).alignof);
    static assert(passNormalY || passAbnormalY && double.alignof <= int.alignof);
}

/*--*
First-class reference type
*/
struct Ref(T)
{
    private T * _p;
    this(ref T value) { _p = &value; }
    ref T opDot() { return *_p; }
    /*ref*/ T opImplicitCastTo() { return *_p; }
    @property ref T value() { return *_p; }

    void opAssign(T value)
    {
        *_p = value;
    }
    void opAssign(T * value)
    {
        _p = value;
    }
}

unittest
{
    Ref!(int) x;
    int y = 42;
    x = &y;
    assert(x.value == 42);
    x = 5;
    assert(x.value == 5);
    assert(y == 5);
}

/**
Defines a value paired with a distinctive "null" state that denotes
the absence of a value. If default constructed, a $(D
Nullable!T) object starts in the null state. Assigning it renders it
non-null. Calling $(D nullify) can nullify it again.

Example:
----
Nullable!int a;
assert(a.isNull);
a = 5;
assert(!a.isNull);
assert(a == 5);
----

Practically $(D Nullable!T) stores a $(D T) and a $(D bool).
 */
struct Nullable(T)
{
    private T _value;
    private bool _isNull = true;

/**
Constructor initializing $(D this) with $(D value).
 */
    this(inout T value) inout
    {
        _value = value;
        _isNull = false;
    }

/**
Returns $(D true) if and only if $(D this) is in the null state.
 */
    @property bool isNull() const pure nothrow @safe
    {
        return _isNull;
    }

/**
Forces $(D this) to the null state.
 */
    void nullify()()
    {
        .destroy(_value);
        _isNull = true;
    }

/**
Assigns $(D value) to the internally-held state. If the assignment
succeeds, $(D this) becomes non-null.
 */
    void opAssign()(T value)
    {
        _value = value;
        _isNull = false;
    }

/**
Gets the value. $(D this) must not be in the null state.
This function is also called for the implicit conversion to $(D T).
 */
    @property ref inout(T) get() inout pure nothrow @safe
    {
        enum message = "Called `get' on null Nullable!" ~ T.stringof ~ ".";
        assert(!isNull, message);
        return _value;
    }

/**
Implicitly converts to $(D T).
$(D this) must not be in the null state.
 */
    alias get this;
}

unittest
{
    import std.exception : assertThrown;

    Nullable!int a;
    assert(a.isNull);
    assertThrown!Throwable(a.get);
    a = 5;
    assert(!a.isNull);
    assert(a == 5);
    assert(a != 3);
    assert(a.get != 3);
    a.nullify();
    assert(a.isNull);
    a = 3;
    assert(a == 3);
    a *= 6;
    assert(a == 18);
    a = a;
    assert(a == 18);
    a.nullify();
    assertThrown!Throwable(a += 2);
}
unittest
{
    auto k = Nullable!int(74);
    assert(k == 74);
    k.nullify();
    assert(k.isNull);
}
unittest
{
    static int f(in Nullable!int x) {
        return x.isNull ? 42 : x.get;
    }
    Nullable!int a;
    assert(f(a) == 42);
    a = 8;
    assert(f(a) == 8);
    a.nullify();
    assert(f(a) == 42);
}
unittest
{
    import std.exception : assertThrown;

    static struct S { int x; }
    Nullable!S s;
    assert(s.isNull);
    s = S(6);
    assert(s == S(6));
    assert(s != S(0));
    assert(s.get != S(0));
    s.x = 9190;
    assert(s.x == 9190);
    s.nullify();
    assertThrown!Throwable(s.x = 9441);
}
unittest
{
    // Ensure Nullable can be used in pure/nothrow/@safe environment.
    function() pure nothrow @safe
    {
        Nullable!int n;
        assert(n.isNull);
        n = 4;
        assert(!n.isNull);
        assert(n == 4);
        n.nullify();
        assert(n.isNull);
    }();
}
unittest
{
    // Ensure Nullable can be used when the value is not pure/nothrow/@safe
    static struct S
    {
        int x;
        this(this) @system {}
    }

    Nullable!S s;
    assert(s.isNull);
    s = S(5);
    assert(!s.isNull);
    assert(s.x == 5);
    s.nullify();
    assert(s.isNull);
}
unittest
{
    // Bugzilla 9404
    alias N = Nullable!int;

    void foo(N a)
    {
        N b;
        b = a; // `N b = a;` works fine
    }
    N n;
    foo(n);
}
unittest
{
    //Check nullable immutable is constructable
    {
        auto a1 = Nullable!(immutable int)();
        auto a2 = Nullable!(immutable int)(1);
        auto i = a2.get;
    }
    //Check immutable nullable is constructable
    {
        auto a1 = immutable (Nullable!int)();
        auto a2 = immutable (Nullable!int)(1);
        auto i = a2.get;
    }
}
unittest
{
    alias NInt   = Nullable!int;

    //Construct tests
    {
        //from other Nullable null
        NInt a1;
        NInt b1 = a1;
        assert(b1.isNull);

        //from other Nullable non-null
        NInt a2 = NInt(1);
        NInt b2 = a2;
        assert(b2 == 1);

        //Construct from similar nullable
        auto a3 = immutable(NInt)();
        NInt b3 = a3;
        assert(b3.isNull);
    }

    //Assign tests
    {
        //from other Nullable null
        NInt a1;
        NInt b1;
        b1 = a1;
        assert(b1.isNull);

        //from other Nullable non-null
        NInt a2 = NInt(1);
        NInt b2;
        b2 = a2;
        assert(b2 == 1);

        //Construct from similar nullable
        auto a3 = immutable(NInt)();
        NInt b3 = a3;
        b3 = a3;
        assert(b3.isNull);
    }
}
unittest
{
    //Check nullable is nicelly embedable in a struct
    static struct S1
    {
        Nullable!int ni;
    }
    static struct S2 //inspired from 9404
    {
        Nullable!int ni;
        this(S2 other)
        {
            ni = other.ni;
        }
        void opAssign(S2 other)
        {
            ni = other.ni;
        }
    }
    foreach (S; TypeTuple!(S1, S2))
    {
        S a;
        S b = a;
        S c;
        c = a;
    }
}
unittest
{
    // Bugzilla 10268
    import std.json;
    JSONValue value = null;
    auto na = Nullable!JSONValue(value);

    struct S1 { int val; }
    struct S2 { int* val; }
    struct S3 { immutable int* val; }

    {
        auto sm = S1(1);
        immutable si = immutable S1(1);
        static assert( __traits(compiles, { auto x1 =           Nullable!S1(sm); }));
        static assert( __traits(compiles, { auto x2 = immutable Nullable!S1(sm); }));
        static assert( __traits(compiles, { auto x3 =           Nullable!S1(si); }));
        static assert( __traits(compiles, { auto x4 = immutable Nullable!S1(si); }));
    }

    auto nm = 10;
    immutable ni = 10;

    {
        auto sm = S2(&nm);
        immutable si = immutable S2(&ni);
        static assert( __traits(compiles, { auto x =           Nullable!S2(sm); }));
        static assert(!__traits(compiles, { auto x = immutable Nullable!S2(sm); }));
        static assert(!__traits(compiles, { auto x =           Nullable!S2(si); }));
        static assert( __traits(compiles, { auto x = immutable Nullable!S2(si); }));
    }

    {
        auto sm = S3(&ni);
        immutable si = immutable S3(&ni);
        static assert( __traits(compiles, { auto x =           Nullable!S3(sm); }));
        static assert( __traits(compiles, { auto x = immutable Nullable!S3(sm); }));
        static assert( __traits(compiles, { auto x =           Nullable!S3(si); }));
        static assert( __traits(compiles, { auto x = immutable Nullable!S3(si); }));
    }
}
unittest
{
    // Bugzila 10357
    import std.datetime;
    Nullable!SysTime time = SysTime(0);
}

/**
Just like $(D Nullable!T), except that the null state is defined as a
particular value. For example, $(D Nullable!(uint, uint.max)) is an
$(D uint) that sets aside the value $(D uint.max) to denote a null
state. $(D Nullable!(T, nullValue)) is more storage-efficient than $(D
Nullable!T) because it does not need to store an extra $(D bool).
 */
struct Nullable(T, T nullValue)
{
    private T _value = nullValue;

/**
Constructor initializing $(D this) with $(D value).
 */
    this(T value)
    {
        _value = value;
    }

/**
Returns $(D true) if and only if $(D this) is in the null state.
 */
    @property bool isNull() const
    {
        return _value == nullValue;
    }

/**
Forces $(D this) to the null state.
 */
    void nullify()()
    {
        _value = nullValue;
    }

/**
Assigns $(D value) to the internally-held state. No null checks are
made. Note that the assignment may leave $(D this) in the null state.
 */
    void opAssign()(T value)
    {
        _value = value;
    }

/**
Gets the value. $(D this) must not be in the null state.
This function is also called for the implicit conversion to $(D T).
 */
    @property ref inout(T) get() inout
    {
        //@@@6169@@@: We avoid any call that might evaluate nullValue's %s,
        //Because it might messup get's purity and safety inference.
        enum message = "Called `get' on null Nullable!(" ~ T.stringof ~ ",nullValue).";
        assert(!isNull, message);
        return _value;
    }

/**
Implicitly converts to $(D T).
Gets the value. $(D this) must not be in the null state.
 */
    alias get this;
}

unittest
{
    import std.exception : assertThrown;

    Nullable!(int, int.min) a;
    assert(a.isNull);
    assertThrown!Throwable(a.get);
    a = 5;
    assert(!a.isNull);
    assert(a == 5);
    static assert(a.sizeof == int.sizeof);
}
unittest
{
    auto a = Nullable!(int, int.min)(8);
    assert(a == 8);
    a.nullify();
    assert(a.isNull);
}
unittest
{
    static int f(in Nullable!(int, int.min) x) {
        return x.isNull ? 42 : x.get;
    }
    Nullable!(int, int.min) a;
    assert(f(a) == 42);
    a = 8;
    assert(f(a) == 8);
    a.nullify();
    assert(f(a) == 42);
}
unittest
{
    // Ensure Nullable can be used in pure/nothrow/@safe environment.
    function() pure nothrow @safe
    {
        Nullable!(int, int.min) n;
        assert(n.isNull);
        n = 4;
        assert(!n.isNull);
        assert(n == 4);
        n.nullify();
        assert(n.isNull);
    }();
}
unittest
{
    // Ensure Nullable can be used when the value is not pure/nothrow/@safe
    static struct S
    {
        int x;
        bool opEquals(const S s) const @system { return s.x == x; }
    }

    Nullable!(S, S(711)) s;
    assert(s.isNull);
    s = S(5);
    assert(!s.isNull);
    assert(s.x == 5);
    s.nullify();
    assert(s.isNull);
}
unittest
{
    //Check nullable is nicelly embedable in a struct
    static struct S1
    {
        Nullable!(int, 0) ni;
    }
    static struct S2 //inspired from 9404
    {
        Nullable!(int, 0) ni;
        this(S2 other)
        {
            ni = other.ni;
        }
        void opAssign(S2 other)
        {
            ni = other.ni;
        }
    }
    foreach (S; TypeTuple!(S1, S2))
    {
        S a;
        S b = a;
        S c;
        c = a;
    }
}

/**
Just like $(D Nullable!T), except that the object refers to a value
sitting elsewhere in memory. This makes assignments overwrite the
initially assigned value. Internally $(D NullableRef!T) only stores a
pointer to $(D T) (i.e., $(D Nullable!T.sizeof == (T*).sizeof)).
 */
struct NullableRef(T)
{
    private T* _value;

/**
Constructor binding $(D this) with $(D value).
 */
    this(T* value) pure nothrow @safe
    {
        _value = value;
    }

/**
Binds the internal state to $(D value).
 */
    void bind(T* value) pure nothrow @safe
    {
        _value = value;
    }

/**
Returns $(D true) if and only if $(D this) is in the null state.
 */
    @property bool isNull() const pure nothrow @safe
    {
        return _value is null;
    }

/**
Forces $(D this) to the null state.
 */
    void nullify() pure nothrow @safe
    {
        _value = null;
    }

/**
Assigns $(D value) to the internally-held state.
 */
    void opAssign()(T value)
        if (isAssignable!T) //@@@9416@@@
    {
        enum message = "Called `opAssign' on null NullableRef!" ~ T.stringof ~ ".";
        assert(!isNull, message);
        *_value = value;
    }

/**
Gets the value. $(D this) must not be in the null state.
This function is also called for the implicit conversion to $(D T).
 */
    @property ref inout(T) get() inout pure nothrow @safe
    {
        enum message = "Called `get' on null NullableRef!" ~ T.stringof ~ ".";
        assert(!isNull, message);
        return *_value;
    }

/**
Implicitly converts to $(D T).
$(D this) must not be in the null state.
 */
    alias get this;
}

unittest
{
    import std.exception : assertThrown;

    int x = 5, y = 7;
    auto a = NullableRef!(int)(&x);
    assert(!a.isNull);
    assert(a == 5);
    assert(x == 5);
    a = 42;
    assert(x == 42);
    assert(!a.isNull);
    assert(a == 42);
    a.nullify();
    assert(x == 42);
    assert(a.isNull);
    assertThrown!Throwable(a.get);
    assertThrown!Throwable(a = 71);
    a.bind(&y);
    assert(a == 7);
    y = 135;
    assert(a == 135);
}
unittest
{
    static int f(in NullableRef!int x) {
        return x.isNull ? 42 : x.get;
    }
    int x = 5;
    auto a = NullableRef!int(&x);
    assert(f(a) == 5);
    a.nullify();
    assert(f(a) == 42);
}
unittest
{
    // Ensure NullableRef can be used in pure/nothrow/@safe environment.
    function() pure nothrow @safe
    {
        auto storage = new int;
        *storage = 19902;
        NullableRef!int n;
        assert(n.isNull);
        n.bind(storage);
        assert(!n.isNull);
        assert(n == 19902);
        n = 2294;
        assert(n == 2294);
        assert(*storage == 2294);
        n.nullify();
        assert(n.isNull);
    }();
}
unittest
{
    // Ensure NullableRef can be used when the value is not pure/nothrow/@safe
    static struct S
    {
        int x;
        this(this) @system {}
        bool opEquals(const S s) const @system { return s.x == x; }
    }

    auto storage = S(5);

    NullableRef!S s;
    assert(s.isNull);
    s.bind(&storage);
    assert(!s.isNull);
    assert(s.x == 5);
    s.nullify();
    assert(s.isNull);
}
unittest
{
    //Check nullable is nicelly embedable in a struct
    static struct S1
    {
        NullableRef!int ni;
    }
    static struct S2 //inspired from 9404
    {
        NullableRef!int ni;
        this(S2 other)
        {
            ni = other.ni;
        }
        void opAssign(S2 other)
        {
            ni = other.ni;
        }
    }
    foreach (S; TypeTuple!(S1, S2))
    {
        S a;
        S b = a;
        S c;
        c = a;
    }
}

/**
$(D BlackHole!Base) is a subclass of $(D Base) which automatically implements
all abstract member functions in $(D Base) as do-nothing functions.  Each
auto-implemented function just returns the default value of the return type
without doing anything.

The name came from
$(WEB search.cpan.org/~sburke/Class-_BlackHole-0.04/lib/Class/_BlackHole.pm, Class::_BlackHole)
Perl module by Sean M. Burke.

Example:
--------------------
abstract class C
{
    int m_value;
    this(int v) { m_value = v; }
    int value() @property { return m_value; }

    abstract real realValue() @property;
    abstract void doSomething();
}

void main()
{
    auto c = new BlackHole!C(42);
    writeln(c.value);     // prints "42"

    // Abstract functions are implemented as do-nothing:
    writeln(c.realValue); // prints "NaN"
    c.doSomething();      // does nothing
}
--------------------

See_Also:
  AutoImplement, generateEmptyFunction
 */
alias BlackHole(Base) = AutoImplement!(Base, generateEmptyFunction, isAbstractFunction);

unittest
{
    import std.math : isNaN;

    // return default
    {
        interface I_1 { real test(); }
        auto o = new BlackHole!I_1;
        assert(o.test().isNaN); // NaN
    }
    // doc example
    {
        static class C
        {
            int m_value;
            this(int v) { m_value = v; }
            int value() @property { return m_value; }

            abstract real realValue() @property;
            abstract void doSomething();
        }

        auto c = new BlackHole!C(42);
        assert(c.value == 42);

        assert(c.realValue.isNaN); // NaN
        c.doSomething();
    }

    // Bugzilla 12058
    interface Foo
    {
        inout(Object) foo() inout;
    }
    BlackHole!Foo o;
}


/**
$(D WhiteHole!Base) is a subclass of $(D Base) which automatically implements
all abstract member functions as throw-always functions.  Each auto-implemented
function fails with throwing an $(D Error) and does never return.  Useful for
trapping use of not-yet-implemented functions.

The name came from
$(WEB search.cpan.org/~mschwern/Class-_WhiteHole-0.04/lib/Class/_WhiteHole.pm, Class::_WhiteHole)
Perl module by Michael G Schwern.

Example:
--------------------
class C
{
    abstract void notYetImplemented();
}

void main()
{
    auto c = new WhiteHole!C;
    c.notYetImplemented(); // throws an Error
}
--------------------

See_Also:
  AutoImplement, generateAssertTrap
 */
alias WhiteHole(Base) = AutoImplement!(Base, generateAssertTrap, isAbstractFunction);

// / ditto
class NotImplementedError : Error
{
    this(string method)
    {
        super(method ~ " is not implemented");
    }
}

unittest
{
    import std.exception : assertThrown;
    // nothrow
    {
        interface I_1
        {
            void foo();
            void bar() nothrow;
        }
        auto o = new WhiteHole!I_1;
        assertThrown!NotImplementedError(o.foo());
        assertThrown!NotImplementedError(o.bar());
    }
    // doc example
    {
        static class C
        {
            abstract void notYetImplemented();
        }

        auto c = new WhiteHole!C;
        try
        {
            c.notYetImplemented();
            assert(0);
        }
        catch (Error e) {}
    }
}


/**
$(D AutoImplement) automatically implements (by default) all abstract member
functions in the class or interface $(D Base) in specified way.

Params:
  how  = template which specifies _how functions will be implemented/overridden.

         Two arguments are passed to $(D how): the type $(D Base) and an alias
         to an implemented function.  Then $(D how) must return an implemented
         function body as a string.

         The generated function body can use these keywords:
         $(UL
            $(LI $(D a0), $(D a1), &hellip;: arguments passed to the function;)
            $(LI $(D args): a tuple of the arguments;)
            $(LI $(D self): an alias to the function itself;)
            $(LI $(D parent): an alias to the overridden function (if any).)
         )

        You may want to use templated property functions (instead of Implicit
        Template Properties) to generate complex functions:
--------------------
// Prints log messages for each call to overridden functions.
string generateLogger(C, alias fun)() @property
{
    import std.traits;
    enum qname = C.stringof ~ "." ~ __traits(identifier, fun);
    string stmt;

    stmt ~= q{ struct Importer { import std.stdio; } };
    stmt ~= `Importer.writeln$(LPAREN)"Log: ` ~ qname ~ `(", args, ")"$(RPAREN);`;
    static if (!__traits(isAbstractFunction, fun))
    {
        static if (is(ReturnType!fun == void))
            stmt ~= q{ parent(args); };
        else
            stmt ~= q{
                auto r = parent(args);
                Importer.writeln("--> ", r);
                return r;
            };
    }
    return stmt;
}
--------------------

  what = template which determines _what functions should be
         implemented/overridden.

         An argument is passed to $(D what): an alias to a non-final member
         function in $(D Base).  Then $(D what) must return a boolean value.
         Return $(D true) to indicate that the passed function should be
         implemented/overridden.

--------------------
// Sees if fun returns something.
enum bool hasValue(alias fun) = !is(ReturnType!(fun) == void);
--------------------


Note:

Generated code is inserted in the scope of $(D std.typecons) module.  Thus,
any useful functions outside $(D std.typecons) cannot be used in the generated
code.  To workaround this problem, you may $(D import) necessary things in a
local struct, as done in the $(D generateLogger()) template in the above
example.


BUGS:

$(UL
 $(LI Variadic arguments to constructors are not forwarded to super.)
 $(LI Deep interface inheritance causes compile error with messages like
      "Error: function std.typecons._AutoImplement!(Foo)._AutoImplement.bar
      does not override any function".  [$(BUGZILLA 2525), $(BUGZILLA 3525)] )
 $(LI The $(D parent) keyword is actually a delegate to the super class'
      corresponding member function.  [$(BUGZILLA 2540)] )
 $(LI Using alias template parameter in $(D how) and/or $(D what) may cause
     strange compile error.  Use template tuple parameter instead to workaround
     this problem.  [$(BUGZILLA 4217)] )
)
 */
class AutoImplement(Base, alias how, alias what = isAbstractFunction) : Base
{
    private alias autoImplement_helper_ =
        AutoImplement_Helper!("autoImplement_helper_", "Base", Base, how, what);
    mixin(autoImplement_helper_.code);
}

/*
 * Code-generating stuffs are encupsulated in this helper template so that
 * namespace pollusion, which can cause name confliction with Base's public
 * members, should be minimized.
 */
private template AutoImplement_Helper(string myName, string baseName,
        Base, alias generateMethodBody, alias cherrypickMethod)
{
private static:
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Internal stuffs
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    // this would be deprecated by std.typelist.Filter
    template staticFilter(alias pred, lst...)
    {
        static if (lst.length > 0)
        {
            alias tail = staticFilter!(pred, lst[1 .. $]);
            //
            static if (pred!(lst[0]))
                alias staticFilter = TypeTuple!(lst[0], tail);
            else
                alias staticFilter = tail;
        }
        else
            alias staticFilter = TypeTuple!();
    }

    // Returns function overload sets in the class C, filtered with pred.
    template enumerateOverloads(C, alias pred)
    {
        template Impl(names...)
        {
            static if (names.length > 0)
            {
                alias methods = staticFilter!(pred, MemberFunctionsTuple!(C, names[0]));
                alias next = Impl!(names[1 .. $]);

                static if (methods.length > 0)
                    alias Impl = TypeTuple!(OverloadSet!(names[0], methods), next);
                else
                    alias Impl = next;
            }
            else
                alias Impl = TypeTuple!();
        }

        alias enumerateOverloads = Impl!(__traits(allMembers, C));
    }

    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Target functions
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    // Add a non-final check to the cherrypickMethod.
    enum bool canonicalPicker(fun.../+[BUG 4217]+/) =
        !__traits(isFinalFunction, fun[0]) && cherrypickMethod!(fun);

    /*
     * A tuple of overload sets, each item of which consists of functions to be
     * implemented by the generated code.
     */
    alias targetOverloadSets = enumerateOverloads!(Base, canonicalPicker);

    /*
     * A tuple of the super class' constructors.  Used for forwarding
     * constructor calls.
     */
    static if (__traits(hasMember, Base, "__ctor"))
        alias ctorOverloadSet = OverloadSet!("__ctor", __traits(getOverloads, Base, "__ctor"));
    else
        alias ctorOverloadSet = OverloadSet!("__ctor"); // empty


    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Type information
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    /*
     * The generated code will be mixed into AutoImplement, which will be
     * instantiated in this module's scope.  Thus, any user-defined types are
     * out of scope and cannot be used directly (i.e. by their names).
     *
     * We will use FuncInfo instances for accessing return types and parameter
     * types of the implemented functions.  The instances will be populated to
     * the AutoImplement's scope in a certain way; see the populate() below.
     */

    // Returns the preferred identifier for the FuncInfo instance for the i-th
    // overloaded function with the name.
    template INTERNAL_FUNCINFO_ID(string name, size_t i)
    {
        import std.string : format;

        enum string INTERNAL_FUNCINFO_ID = format("F_%s_%s", name, i);
    }

    /*
     * Insert FuncInfo instances about all the target functions here.  This
     * enables the generated code to access type information via, for example,
     * "autoImplement_helper_.F_foo_1".
     */
    template populate(overloads...)
    {
        static if (overloads.length > 0)
        {
            mixin populate!(overloads[0].name, overloads[0].contents);
            mixin populate!(overloads[1 .. $]);
        }
    }
    template populate(string name, methods...)
    {
        static if (methods.length > 0)
        {
            mixin populate!(name, methods[0 .. $ - 1]);
            //
            alias target = methods[$ - 1];
            enum ith = methods.length - 1;
            mixin("alias " ~ INTERNAL_FUNCINFO_ID!(name, ith) ~ " = FuncInfo!target;");
        }
    }

    public mixin populate!(targetOverloadSets);
    public mixin populate!(  ctorOverloadSet );


    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Code-generating policies
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    /* Common policy configurations for generating constructors and methods. */
    template CommonGeneratingPolicy()
    {
        // base class identifier which generated code should use
        enum string BASE_CLASS_ID = baseName;

        // FuncInfo instance identifier which generated code should use
        template FUNCINFO_ID(string name, size_t i)
        {
            enum string FUNCINFO_ID =
                myName ~ "." ~ INTERNAL_FUNCINFO_ID!(name, i);
        }
    }

    /* Policy configurations for generating constructors. */
    template ConstructorGeneratingPolicy()
    {
        mixin CommonGeneratingPolicy;

        /* Generates constructor body.  Just forward to the base class' one. */
        string generateFunctionBody(ctor.../+[BUG 4217]+/)() @property
        {
            enum varstyle = variadicFunctionStyle!(typeof(&ctor[0]));

            static if (varstyle & (Variadic.c | Variadic.d))
            {
                // the argptr-forwarding problem
                //pragma(msg, "Warning: AutoImplement!(", Base, ") ",
                //        "ignored variadic arguments to the constructor ",
                //        FunctionTypeOf!(typeof(&ctor[0])) );
            }
            return "super(args);";
        }
    }

    /* Policy configurations for genearting target methods. */
    template MethodGeneratingPolicy()
    {
        mixin CommonGeneratingPolicy;

        /* Geneartes method body. */
        string generateFunctionBody(func.../+[BUG 4217]+/)() @property
        {
            return generateMethodBody!(Base, func); // given
        }
    }


    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Generated code
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    alias ConstructorGenerator = MemberFunctionGenerator!(ConstructorGeneratingPolicy!());
    alias MethodGenerator      = MemberFunctionGenerator!(MethodGeneratingPolicy!());

    public enum string code =
        ConstructorGenerator.generateCode!(  ctorOverloadSet ) ~ "\n" ~
             MethodGenerator.generateCode!(targetOverloadSets);

    debug (SHOW_GENERATED_CODE)
    {
        pragma(msg, "-------------------- < ", Base, " >");
        pragma(msg, code);
        pragma(msg, "--------------------");
    }
}

//debug = SHOW_GENERATED_CODE;
version(unittest) import core.vararg;
unittest
{
    // no function to implement
    {
        interface I_1 {}
        auto o = new BlackHole!I_1;
    }
    // parameters
    {
        interface I_3 { void test(int, in int, out int, ref int, lazy int); }
        auto o = new BlackHole!I_3;
    }
    // use of user-defined type
    {
        struct S {}
        interface I_4 { S test(); }
        auto o = new BlackHole!I_4;
    }
    // overloads
    {
        interface I_5
        {
            void test(string);
            real test(real);
            int  test();
        }
        auto o = new BlackHole!I_5;
    }
    // constructor forwarding
    {
        static class C_6
        {
            this(int n) { assert(n == 42); }
            this(string s) { assert(s == "Deeee"); }
            this(...) {}
        }
        auto o1 = new BlackHole!C_6(42);
        auto o2 = new BlackHole!C_6("Deeee");
        auto o3 = new BlackHole!C_6(1, 2, 3, 4);
    }
    // attributes
    {
        interface I_7
        {
            ref int test_ref();
            int test_pure() pure;
            int test_nothrow() nothrow;
            int test_property() @property;
            int test_safe() @safe;
            int test_trusted() @trusted;
            int test_system() @system;
            int test_pure_nothrow() pure nothrow;
        }
        auto o = new BlackHole!I_7;
    }
    // storage classes
    {
        interface I_8
        {
            void test_const() const;
            void test_immutable() immutable;
            void test_shared() shared;
            void test_shared_const() shared const;
        }
        auto o = new BlackHole!I_8;
    }
    /+ // deep inheritance
    {
    // XXX [BUG 2525,3525]
    // NOTE: [r494] func.c(504-571) FuncDeclaration::semantic()
        interface I { void foo(); }
        interface J : I {}
        interface K : J {}
        static abstract class C_9 : K {}
        auto o = new BlackHole!C_9;
    }+/
}

version(unittest)
{
    // Issue 10647
    private string generateDoNothing(C, alias fun)() @property
    {
        string stmt;

        static if (is(ReturnType!fun == void))
            stmt ~= "";
        else
        {
            string returnType = ReturnType!fun.stringof;
            stmt ~= "return "~returnType~".init;";
        }
        return stmt;
    }

    private template isAlwaysTrue(alias fun)
    {
        enum isAlwaysTrue = true;
    }

    // Do nothing template
    private template DoNothing(Base)
    {
        alias DoNothing = AutoImplement!(Base, generateDoNothing, isAlwaysTrue);
    }

    // A class to be overridden
    private class Foo{
        void bar(int a) { }
    }
}
unittest
{
    auto foo = new DoNothing!Foo();
    foo.bar(13);
}

/*
Used by MemberFunctionGenerator.
 */
package template OverloadSet(string nam, T...)
{
    enum string name = nam;
    alias contents = T;
}

/*
Used by MemberFunctionGenerator.
 */
package template FuncInfo(alias func, /+[BUG 4217 ?]+/ T = typeof(&func))
{
    alias RT =         ReturnType!T;
    alias PT = ParameterTypeTuple!T;
}
package template FuncInfo(Func)
{
    alias RT =         ReturnType!Func;
    alias PT = ParameterTypeTuple!Func;
}

/*
General-purpose member function generator.
--------------------
template GeneratingPolicy()
{
    // [optional] the name of the class where functions are derived
    enum string BASE_CLASS_ID;

    // [optional] define this if you have only function types
    enum bool WITHOUT_SYMBOL;

    // [optional] Returns preferred identifier for i-th parameter.
    template PARAMETER_VARIABLE_ID(size_t i);

    // Returns the identifier of the FuncInfo instance for the i-th overload
    // of the specified name.  The identifier must be accessible in the scope
    // where generated code is mixed.
    template FUNCINFO_ID(string name, size_t i);

    // Returns implemented function body as a string.  When WITHOUT_SYMBOL is
    // defined, the latter is used.
    template generateFunctionBody(alias func);
    template generateFunctionBody(string name, FuncType);
}
--------------------
 */
package template MemberFunctionGenerator(alias Policy)
{
private static:
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Internal stuffs
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    import std.string;

    enum CONSTRUCTOR_NAME = "__ctor";

    // true if functions are derived from a base class
    enum WITH_BASE_CLASS = __traits(hasMember, Policy, "BASE_CLASS_ID");

    // true if functions are specified as types, not symbols
    enum WITHOUT_SYMBOL = __traits(hasMember, Policy, "WITHOUT_SYMBOL");

    // preferred identifier for i-th parameter variable
    static if (__traits(hasMember, Policy, "PARAMETER_VARIABLE_ID"))
    {
        alias PARAMETER_VARIABLE_ID = Policy.PARAMETER_VARIABLE_ID;
    }
    else
    {
        enum string PARAMETER_VARIABLE_ID(size_t i) = format("a%s", i);
            // default: a0, a1, ...
    }

    // Returns a tuple consisting of 0,1,2,...,n-1.  For static foreach.
    template CountUp(size_t n)
    {
        static if (n > 0)
            alias CountUp = TypeTuple!(CountUp!(n - 1), n - 1);
        else
            alias CountUp = TypeTuple!();
    }


    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://
    // Code generator
    //:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::://

    /*
     * Runs through all the target overload sets and generates D code which
     * implements all the functions in the overload sets.
     */
    public string generateCode(overloads...)() @property
    {
        string code = "";

        // run through all the overload sets
        foreach (i_; CountUp!(0 + overloads.length)) // workaround
        {
            enum i = 0 + i_; // workaround
            alias oset = overloads[i];

            code ~= generateCodeForOverloadSet!(oset);

            static if (WITH_BASE_CLASS && oset.name != CONSTRUCTOR_NAME)
            {
                // The generated function declarations may hide existing ones
                // in the base class (cf. HiddenFuncError), so we put an alias
                // declaration here to reveal possible hidden functions.
                code ~= format("alias %s = %s.%s;\n",
                            oset.name,
                            Policy.BASE_CLASS_ID, // [BUG 2540] super.
                            oset.name);
            }
        }
        return code;
    }

    // handle each overload set
    private string generateCodeForOverloadSet(alias oset)() @property
    {
        string code = "";

        foreach (i_; CountUp!(0 + oset.contents.length)) // workaround
        {
            enum i = 0 + i_; // workaround
            code ~= generateFunction!(
                    Policy.FUNCINFO_ID!(oset.name, i), oset.name,
                    oset.contents[i]) ~ "\n";
        }
        return code;
    }

    /*
     * Returns D code which implements the function func.  This function
     * actually generates only the declarator part; the function body part is
     * generated by the functionGenerator() policy.
     */
    public string generateFunction(
            string myFuncInfo, string name, func... )() @property
    {
        import std.string : format;

        enum isCtor = (name == CONSTRUCTOR_NAME);

        string code; // the result

        /*** Function Declarator ***/
        {
            alias Func = FunctionTypeOf!(func);
            alias FA = FunctionAttribute;
            enum atts     = functionAttributes!(func);
            enum realName = isCtor ? "this" : name;

            // FIXME?? Make it so that these aren't CTFE funcs any more, since
            // Format is deprecated, and format works at compile time?
            /* Made them CTFE funcs just for the sake of Format!(...) */

            // return type with optional "ref"
            static string make_returnType()
            {
                string rtype = "";

                if (!isCtor)
                {
                    if (atts & FA.ref_) rtype ~= "ref ";
                    rtype ~= myFuncInfo ~ ".RT";
                }
                return rtype;
            }
            enum returnType = make_returnType();

            // function attributes attached after declaration
            static string make_postAtts()
            {
                string poatts = "";
                if (atts & FA.pure_   ) poatts ~= " pure";
                if (atts & FA.nothrow_) poatts ~= " nothrow";
                if (atts & FA.property) poatts ~= " @property";
                if (atts & FA.safe    ) poatts ~= " @safe";
                if (atts & FA.trusted ) poatts ~= " @trusted";
                return poatts;
            }
            enum postAtts = make_postAtts();

            // function storage class
            static string make_storageClass()
            {
                string postc = "";
                if (is(Func ==    shared)) postc ~= " shared";
                if (is(Func ==     const)) postc ~= " const";
                if (is(Func ==     inout)) postc ~= " inout";
                if (is(Func == immutable)) postc ~= " immutable";
                return postc;
            }
            enum storageClass = make_storageClass();

            //
            if (__traits(isVirtualMethod, func))
                code ~= "override ";
            code ~= format("extern(%s) %s %s(%s) %s %s\n",
                    functionLinkage!(func),
                    returnType,
                    realName,
                    generateParameters!(myFuncInfo, func)(),
                    postAtts, storageClass );
        }

        /*** Function Body ***/
        code ~= "{\n";
        {
            enum nparams = ParameterTypeTuple!(func).length;

            /* Declare keywords: args, self and parent. */
            string preamble;

            preamble ~= "alias args = TypeTuple!(" ~ enumerateParameters!(nparams) ~ ");\n";
            if (!isCtor)
            {
                preamble ~= "alias self = " ~ name ~ ";\n";
                if (WITH_BASE_CLASS && !__traits(isAbstractFunction, func))
                    //preamble ~= "alias super." ~ name ~ " parent;\n"; // [BUG 2540]
                    preamble ~= "auto parent = &super." ~ name ~ ";\n";
            }

            // Function body
            static if (WITHOUT_SYMBOL)
                enum fbody = Policy.generateFunctionBody!(name, func);
            else
                enum fbody = Policy.generateFunctionBody!(func);

            code ~= preamble;
            code ~= fbody;
        }
        code ~= "}";

        return code;
    }

    /*
     * Returns D code which declares function parameters.
     * "ref int a0, real a1, ..."
     */
    private string generateParameters(string myFuncInfo, func...)()
    {
        alias STC = ParameterStorageClass;
        alias stcs = ParameterStorageClassTuple!(func);
        enum nparams = stcs.length;

        string params = ""; // the result

        foreach (i, stc; stcs)
        {
            if (i > 0) params ~= ", ";

            // Parameter storage classes.
            if (stc & STC.scope_) params ~= "scope ";
            if (stc & STC.out_  ) params ~= "out ";
            if (stc & STC.ref_  ) params ~= "ref ";
            if (stc & STC.lazy_ ) params ~= "lazy ";

            // Take parameter type from the FuncInfo.
            params ~= format("%s.PT[%s]", myFuncInfo, i);

            // Declare a parameter variable.
            params ~= " " ~ PARAMETER_VARIABLE_ID!(i);
        }

        // Add some ellipsis part if needed.
        final switch (variadicFunctionStyle!(func))
        {
            case Variadic.no:
                break;

            case Variadic.c, Variadic.d:
                // (...) or (a, b, ...)
                params ~= (nparams == 0) ? "..." : ", ...";
                break;

            case Variadic.typesafe:
                params ~= " ...";
                break;
        }

        return params;
    }

    // Returns D code which enumerates n parameter variables using comma as the
    // separator.  "a0, a1, a2, a3"
    private string enumerateParameters(size_t n)() @property
    {
        string params = "";

        foreach (i_; CountUp!(n))
        {
            enum i = 0 + i_; // workaround
            if (i > 0) params ~= ", ";
            params ~= PARAMETER_VARIABLE_ID!(i);
        }
        return params;
    }
}


/**
Predefined how-policies for $(D AutoImplement).  These templates are used by
$(D BlackHole) and $(D WhiteHole), respectively.
 */
template generateEmptyFunction(C, func.../+[BUG 4217]+/)
{
    static if (is(ReturnType!(func) == void))
        enum string generateEmptyFunction = q{
        };
    else static if (functionAttributes!(func) & FunctionAttribute.ref_)
        enum string generateEmptyFunction = q{
            static typeof(return) dummy;
            return dummy;
        };
    else
        enum string generateEmptyFunction = q{
            return typeof(return).init;
        };
}

/// ditto
template generateAssertTrap(C, func...)
{
    enum string generateAssertTrap =
        `throw new NotImplementedError("` ~ C.stringof ~ "."
                ~ __traits(identifier, func) ~ `");`;
}

private
{
    pragma(mangle, "_d_toObject")
    extern(C) pure nothrow Object typecons_d_toObject(void* p);
}

/*
 * Avoids opCast operator overloading.
 */
private template dynamicCast(T)
if (is(T == class) || is(T == interface))
{
    @trusted
    T dynamicCast(S)(inout S source)
    if (is(S == class) || is(S == interface))
    {
        static if (is(Unqual!S : Unqual!T))
        {
            import std.traits : QualifierOf;
            alias Qual = QualifierOf!S; // SharedOf or MutableOf
            alias TmpT = Qual!(Unqual!T);
            inout(TmpT) tmp = source;   // bypass opCast by implicit conversion
            return *cast(T*)(&tmp);     // + variable pointer cast + dereference
        }
        else
        {
            return cast(T)typecons_d_toObject(*cast(void**)(&source));
        }
    }
}

unittest
{
    class C { @disable opCast(T)() {} }
    auto c = new C;
    static assert(!__traits(compiles, cast(Object)c));
    auto o = dynamicCast!Object(c);
    assert(c is o);

    interface I { @disable opCast(T)() {} Object instance(); }
    interface J { @disable opCast(T)() {} Object instance(); }
    class D : I, J { Object instance() { return this; } }
    I i = new D();
    static assert(!__traits(compiles, cast(J)i));
    J j = dynamicCast!J(i);
    assert(i.instance() is j.instance());
}

/**
 * Supports structural based typesafe conversion.
 *
 * If $(D Source) has structural conformance with the $(D interface) $(D Targets),
 * wrap creates internal wrapper class which inherits $(D Targets) and
 * wrap $(D src) object, then return it.
 */
template wrap(Targets...)
if (Targets.length >= 1 && allSatisfy!(isMutable, Targets))
{
    import std.typetuple : staticMap;

    // strict upcast
    auto wrap(Source)(inout Source src) @trusted pure nothrow
    if (Targets.length == 1 && is(Source : Targets[0]))
    {
        alias T = Select!(is(Source == shared), shared Targets[0], Targets[0]);
        return dynamicCast!(inout T)(src);
    }
    // structural upcast
    template wrap(Source)
    if (!allSatisfy!(Bind!(isImplicitlyConvertible, Source), Targets))
    {
        auto wrap(inout Source src)
        {
            static assert(hasRequireMethods!(),
                          "Source "~Source.stringof~
                          " does not have structural conformance to "~
                          Targets.stringof);

            alias T = Select!(is(Source == shared), shared Impl, Impl);
            return new inout T(src);
        }

        template FuncInfo(string s, F)
        {
            enum name = s;
            alias type = F;
        }

        // Concat all Targets function members into one tuple
        template Concat(size_t i = 0)
        {
            static if (i >= Targets.length)
                alias Concat = TypeTuple!();
            else
            {
                alias Concat = TypeTuple!(GetOverloadedMethods!(Targets[i]), Concat!(i + 1));
            }
        }
        // Remove duplicated functions based on the identifier name and function type covariance
        template Uniq(members...)
        {
            static if (members.length == 0)
                alias Uniq = TypeTuple!();
            else
            {
                alias func = members[0];
                enum  name = __traits(identifier, func);
                alias type = FunctionTypeOf!func;
                template check(size_t i, mem...)
                {
                    static if (i >= mem.length)
                        enum ptrdiff_t check = -1;
                    else
                    {
                        enum ptrdiff_t check =
                            __traits(identifier, func) == __traits(identifier, mem[i]) &&
                            !is(DerivedFunctionType!(type, FunctionTypeOf!(mem[i])) == void)
                          ? i : check!(i + 1, mem);
                    }
                }
                enum ptrdiff_t x = 1 + check!(0, members[1 .. $]);
                static if (x >= 1)
                {
                    alias typex = DerivedFunctionType!(type, FunctionTypeOf!(members[x]));
                    alias remain = Uniq!(members[1 .. x], members[x + 1 .. $]);

                    static if (remain.length >= 1 && remain[0].name == name &&
                               !is(DerivedFunctionType!(typex, remain[0].type) == void))
                    {
                        alias F = DerivedFunctionType!(typex, remain[0].type);
                        alias Uniq = TypeTuple!(FuncInfo!(name, F), remain[1 .. $]);
                    }
                    else
                        alias Uniq = TypeTuple!(FuncInfo!(name, typex), remain);
                }
                else
                {
                    alias Uniq = TypeTuple!(FuncInfo!(name, type), Uniq!(members[1 .. $]));
                }
            }
        }
        alias TargetMembers = Uniq!(Concat!());             // list of FuncInfo
        alias SourceMembers = GetOverloadedMethods!Source;  // list of function symbols

        // Check whether all of SourceMembers satisfy covariance target in TargetMembers
        template hasRequireMethods(size_t i = 0)
        {
            static if (i >= TargetMembers.length)
                enum hasRequireMethods = true;
            else
            {
                enum hasRequireMethods =
                    findCovariantFunction!(TargetMembers[i], Source, SourceMembers) != -1 &&
                    hasRequireMethods!(i + 1);
            }
        }

        // Internal wrapper class
        final class Impl : Structural, Targets
        {
        private:
            Source _wrap_source;

            this(       inout Source s)        inout @safe pure nothrow { _wrap_source = s; }
            this(shared inout Source s) shared inout @safe pure nothrow { _wrap_source = s; }

            // BUG: making private should work with NVI.
            protected final inout(Object) _wrap_getSource() inout @trusted
            {
                return dynamicCast!(inout Object)(_wrap_source);
            }

            import std.conv : to;
            import std.algorithm : forward;
            template generateFun(size_t i)
            {
                enum name = TargetMembers[i].name;
                enum fa = functionAttributes!(TargetMembers[i].type);
                static @property stc()
                {
                    string r;
                    if (fa & FunctionAttribute.property)    r ~= "@property ";
                    if (fa & FunctionAttribute.ref_)        r ~= "ref ";
                    if (fa & FunctionAttribute.pure_)       r ~= "pure ";
                    if (fa & FunctionAttribute.nothrow_)    r ~= "nothrow ";
                    if (fa & FunctionAttribute.trusted)     r ~= "@trusted ";
                    if (fa & FunctionAttribute.safe)        r ~= "@safe ";
                    return r;
                }
                static @property mod()
                {
                    alias type = TypeTuple!(TargetMembers[i].type)[0];
                    string r;
                    static if (is(type == immutable))       r ~= " immutable";
                    else
                    {
                        static if (is(type == shared))      r ~= " shared";
                        static if (is(type == const))       r ~= " const";
                        else static if (is(type == inout))  r ~= " inout";
                        //else  --> mutable
                    }
                    return r;
                }
                enum n = to!string(i);
                static if (fa & FunctionAttribute.property)
                {
                    static if (ParameterTypeTuple!(TargetMembers[i].type).length == 0)
                        enum fbody = "_wrap_source."~name;
                    else
                        enum fbody = "_wrap_source."~name~" = forward!args";
                }
                else
                {
                        enum fbody = "_wrap_source."~name~"(forward!args)";
                }
                enum generateFun =
                    "override "~stc~"ReturnType!(TargetMembers["~n~"].type) "
                    ~ name~"(ParameterTypeTuple!(TargetMembers["~n~"].type) args) "~mod~
                    "{ return "~fbody~"; }";
            }

        public:
            mixin mixinAll!(
                staticMap!(generateFun, staticIota!(0, TargetMembers.length)));
        }
    }
}
/// ditto
template wrap(Targets...)
if (Targets.length >= 1 && !allSatisfy!(isMutable, Targets))
{
    import std.typetuple : staticMap;

    alias wrap = .wrap!(staticMap!(Unqual, Targets));
}

// Internal class to support dynamic cross-casting
private interface Structural
{
    inout(Object) _wrap_getSource() inout @safe pure nothrow;
}

/**
 * Extract object which wrapped by $(D wrap).
 */
template unwrap(Target)
if (isMutable!Target)
{
    // strict downcast
    auto unwrap(Source)(inout Source src) @trusted pure nothrow
    if (is(Target : Source))
    {
        alias T = Select!(is(Source == shared), shared Target, Target);
        return dynamicCast!(inout T)(src);
    }
    // structural downcast
    auto unwrap(Source)(inout Source src) @trusted pure nothrow
    if (!is(Target : Source))
    {
        alias T = Select!(is(Source == shared), shared Target, Target);
        Object o = dynamicCast!(Object)(src);   // remove qualifier
        do
        {
            if (auto a = dynamicCast!(Structural)(o))
            {
                if (auto d = dynamicCast!(inout T)(o = a._wrap_getSource()))
                    return d;
            }
            else if (auto d = dynamicCast!(inout T)(o))
                return d;
            else
                break;
        } while (o);
        return null;
    }
}
/// ditto
template unwrap(Target)
if (!isMutable!Target)
{
    alias unwrap = .unwrap!(Unqual!Target);
}

///
unittest
{
    interface Quack
    {
        int quack();
        @property int height();
    }
    interface Flyer
    {
        @property int height();
    }
    class Duck : Quack
    {
        int quack() { return 1; }
        @property int height() { return 10; }
    }
    class Human
    {
        int quack() { return 2; }
        @property int height() { return 20; }
    }

    Duck d1 = new Duck();
    Human h1 = new Human();

    interface Refleshable
    {
        int reflesh();
    }
    // does not have structural conformance
    static assert(!__traits(compiles, d1.wrap!Refleshable));
    static assert(!__traits(compiles, h1.wrap!Refleshable));

    // strict upcast
    Quack qd = d1.wrap!Quack;
    assert(qd is d1);
    assert(qd.quack() == 1);    // calls Duck.quack
    // strict downcast
    Duck d2 = qd.unwrap!Duck;
    assert(d2 is d1);

    // structural upcast
    Quack qh = h1.wrap!Quack;
    assert(qh.quack() == 2);    // calls Human.quack
    // structural downcast
    Human h2 = qh.unwrap!Human;
    assert(h2 is h1);

    // structural upcast (two steps)
    Quack qx = h1.wrap!Quack;   // Human -> Quack
    Flyer fx = qx.wrap!Flyer;   // Quack -> Flyer
    assert(fx.height == 20);    // calls Human.height
    // strucural downcast (two steps)
    Quack qy = fx.unwrap!Quack; // Flyer -> Quack
    Human hy = qy.unwrap!Human; // Quack -> Human
    assert(hy is h1);
    // strucural downcast (one step)
    Human hz = fx.unwrap!Human; // Flyer -> Human
    assert(hz is h1);
}
///
unittest
{
    interface A { int run(); }
    interface B { int stop(); @property int status(); }
    class X
    {
        int run() { return 1; }
        int stop() { return 2; }
        @property int status() { return 3; }
    }

    auto x = new X();
    auto ab = x.wrap!(A, B);
    A a = ab;
    B b = ab;
    assert(a.run() == 1);
    assert(b.stop() == 2);
    assert(b.status == 3);
    static assert(functionAttributes!(typeof(ab).status) & FunctionAttribute.property);
}
unittest
{
    class A
    {
        int draw()              { return 1; }
        int draw(int v)         { return v; }

        int draw() const        { return 2; }
        int draw() shared       { return 3; }
        int draw() shared const { return 4; }
        int draw() immutable    { return 5; }
    }
    interface Drawable
    {
        int draw();
        int draw() const;
        int draw() shared;
        int draw() shared const;
        int draw() immutable;
    }
    interface Drawable2
    {
        int draw(int v);
    }

    auto ma = new A();
    auto sa = new shared A();
    auto ia = new immutable A();
    {
                     Drawable  md = ma.wrap!Drawable;
               const Drawable  cd = ma.wrap!Drawable;
              shared Drawable  sd = sa.wrap!Drawable;
        shared const Drawable scd = sa.wrap!Drawable;
           immutable Drawable  id = ia.wrap!Drawable;
        assert( md.draw() == 1);
        assert( cd.draw() == 2);
        assert( sd.draw() == 3);
        assert(scd.draw() == 4);
        assert( id.draw() == 5);
    }
    {
        Drawable2 d = ma.wrap!Drawable2;
        static assert(!__traits(compiles, d.draw()));
        assert(d.draw(10) == 10);
    }
}
unittest
{
    // Bugzilla 10377
    import std.range, std.algorithm;

    interface MyInputRange(T)
    {
        @property T front();
        void popFront();
        @property bool empty();
    }

    //auto o = iota(0,10,1).inputRangeObject();
    //pragma(msg, __traits(allMembers, typeof(o)));
    auto r = iota(0,10,1).inputRangeObject().wrap!(MyInputRange!int)();
    assert(equal(r, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
}
unittest
{
    // Bugzilla 10536
    interface Interface
    {
        int foo();
    }
    class Pluggable
    {
        int foo() { return 1; }
        @disable void opCast(T, this X)();  // !
    }

    Interface i = new Pluggable().wrap!Interface;
    assert(i.foo() == 1);
}
unittest
{
    // Enhancement 10538
    interface Interface
    {
        int foo();
        int bar(int);
    }
    class Pluggable
    {
        int opDispatch(string name, A...)(A args) { return 100; }
    }

    Interface i = wrap!Interface(new Pluggable());
    assert(i.foo() == 100);
    assert(i.bar(10) == 100);
}

// Make a tuple of non-static function symbols
private template GetOverloadedMethods(T)
{
    import std.typetuple : Filter;

    alias allMembers = TypeTuple!(__traits(allMembers, T));
    template follows(size_t i = 0)
    {
        static if (i >= allMembers.length)
        {
            alias follows = TypeTuple!();
        }
        else static if (!__traits(compiles, mixin("T."~allMembers[i])))
        {
            alias follows = follows!(i + 1);
        }
        else
        {
            enum name = allMembers[i];

            template isMethod(alias f)
            {
                static if (is(typeof(&f) F == F*) && is(F == function))
                    enum isMethod = !__traits(isStaticFunction, f);
                else
                    enum isMethod = false;
            }
            alias follows = TypeTuple!(
                std.typetuple.Filter!(isMethod, __traits(getOverloads, T, name)),
                follows!(i + 1));
        }
    }
    alias GetOverloadedMethods = follows!();
}
// find a function from Fs that has same identifier and covariant type with f
private template findCovariantFunction(alias finfo, Source, Fs...)
{
    template check(size_t i = 0)
    {
        static if (i >= Fs.length)
            enum ptrdiff_t check = -1;
        else
        {
            enum ptrdiff_t check =
                (finfo.name == __traits(identifier, Fs[i])) &&
                isCovariantWith!(FunctionTypeOf!(Fs[i]), finfo.type)
              ? i : check!(i + 1);
        }
    }
    enum x = check!();
    static if (x == -1 && is(typeof(Source.opDispatch)))
    {
        alias Params = ParameterTypeTuple!(finfo.type);
        enum ptrdiff_t findCovariantFunction =
            is(typeof((             Source).init.opDispatch!(finfo.name)(Params.init))) ||
            is(typeof((       const Source).init.opDispatch!(finfo.name)(Params.init))) ||
            is(typeof((   immutable Source).init.opDispatch!(finfo.name)(Params.init))) ||
            is(typeof((      shared Source).init.opDispatch!(finfo.name)(Params.init))) ||
            is(typeof((shared const Source).init.opDispatch!(finfo.name)(Params.init)))
          ? ptrdiff_t.max : -1;
    }
    else
        enum ptrdiff_t findCovariantFunction = x;
}

private enum TypeModifier
{
    mutable     = 0,    // type is mutable
    const_      = 1,    // type is const
    immutable_  = 2,    // type is immutable
    shared_     = 4,    // type is shared
    inout_      = 8,    // type is wild
}
private template TypeMod(T)
{
    static if (is(T == immutable))
    {
        enum mod1 = TypeModifier.immutable_;
        enum mod2 = 0;
    }
    else
    {
        enum mod1 = is(T == shared) ? TypeModifier.shared_ : 0;
        static if (is(T == const))
            enum mod2 = TypeModifier.const_;
        else static if (is(T == inout))
            enum mod2 = TypeModifier.inout_;
        else
            enum mod2 = TypeModifier.mutable;
    }
    enum TypeMod = cast(TypeModifier)(mod1 | mod2);
}

version(unittest)
{
    private template UnittestFuncInfo(alias f)
    {
        enum name = __traits(identifier, f);
        alias type = FunctionTypeOf!f;
    }
}
unittest
{
    class A
    {
        int draw() { return 1; }
        @property int value() { return 2; }
        final int run() { return 3; }
    }
    alias methods = GetOverloadedMethods!A;

    alias int F1();
    alias @property int F2();
    alias string F3();
    alias nothrow @trusted uint F4();
    alias int F5(Object);
    alias bool F6(Object);
    static assert(methods.length == 3 + 4);
    static assert(__traits(identifier, methods[0]) == "draw"     && is(typeof(&methods[0]) == F1*));
    static assert(__traits(identifier, methods[1]) == "value"    && is(typeof(&methods[1]) == F2*));
    static assert(__traits(identifier, methods[2]) == "run"      && is(typeof(&methods[2]) == F1*));

    int draw() { return 0; }
    @property int value() { return 0; }
    void opEquals() {}
    int nomatch() { return 0; }
    static assert(findCovariantFunction!(UnittestFuncInfo!draw,     A, methods) == 0);
    static assert(findCovariantFunction!(UnittestFuncInfo!value,    A, methods) == 1);
    static assert(findCovariantFunction!(UnittestFuncInfo!opEquals, A, methods) == -1);
    static assert(findCovariantFunction!(UnittestFuncInfo!nomatch,  A, methods) == -1);

    // considering opDispatch
    class B
    {
        void opDispatch(string name, A...)(A) {}
    }
    alias methodsB = GetOverloadedMethods!B;
    static assert(findCovariantFunction!(UnittestFuncInfo!draw,     B, methodsB) == ptrdiff_t.max);
    static assert(findCovariantFunction!(UnittestFuncInfo!value,    B, methodsB) == ptrdiff_t.max);
    static assert(findCovariantFunction!(UnittestFuncInfo!opEquals, B, methodsB) == ptrdiff_t.max);
    static assert(findCovariantFunction!(UnittestFuncInfo!nomatch,  B, methodsB) == ptrdiff_t.max);
}

private template DerivedFunctionType(T...)
{
    static if (!T.length)
    {
        alias DerivedFunctionType = void;
    }
    else static if (T.length == 1)
    {
        static if (is(T[0] == function))
        {
            alias DerivedFunctionType = T[0];
        }
        else
        {
            alias DerivedFunctionType = void;
        }
    }
    else static if (is(T[0] P0 == function) && is(T[1] P1 == function))
    {
        alias FA = FunctionAttribute;

        alias F0 = T[0], R0 = ReturnType!F0, PSTC0 = ParameterStorageClassTuple!F0;
        alias F1 = T[1], R1 = ReturnType!F1, PSTC1 = ParameterStorageClassTuple!F1;
        enum FA0 = functionAttributes!F0;
        enum FA1 = functionAttributes!F1;

        template CheckParams(size_t i = 0)
        {
            static if (i >= P0.length)
                enum CheckParams = true;
            else
            {
                enum CheckParams = (is(P0[i] == P1[i]) && PSTC0[i] == PSTC1[i]) &&
                                   CheckParams!(i + 1);
            }
        }
        static if (R0.sizeof == R1.sizeof && !is(CommonType!(R0, R1) == void) &&
                   P0.length == P1.length && CheckParams!() && TypeMod!F0 == TypeMod!F1 &&
                   variadicFunctionStyle!F0 == variadicFunctionStyle!F1 &&
                   functionLinkage!F0 == functionLinkage!F1 &&
                   ((FA0 ^ FA1) & (FA.ref_ | FA.property)) == 0)
        {
            alias R = Select!(is(R0 : R1), R0, R1);
            alias FX = FunctionTypeOf!(R function(P0));
            alias FY = SetFunctionAttributes!(FX, functionLinkage!F0, FA0 | FA1);
            alias DerivedFunctionType = DerivedFunctionType!(FY, T[2 .. $]);
        }
        else
            alias DerivedFunctionType = void;
    }
    else
        alias DerivedFunctionType = void;
}
unittest
{
    // attribute covariance
    alias int F1();
    static assert(is(DerivedFunctionType!(F1, F1) == F1));
    alias int F2() pure nothrow;
    static assert(is(DerivedFunctionType!(F1, F2) == F2));
    alias int F3() @safe;
    alias int F23() pure nothrow @safe;
    static assert(is(DerivedFunctionType!(F2, F3) == F23));

    // return type covariance
    alias long F4();
    static assert(is(DerivedFunctionType!(F1, F4) == void));
    class C {}
    class D : C {}
    alias C F5();
    alias D F6();
    static assert(is(DerivedFunctionType!(F5, F6) == F6));
    alias typeof(null) F7();
    alias int[] F8();
    alias int* F9();
    static assert(is(DerivedFunctionType!(F5, F7) == F7));
    static assert(is(DerivedFunctionType!(F7, F8) == void));
    static assert(is(DerivedFunctionType!(F7, F9) == F7));

    // variadic type equality
    alias int F10(int);
    alias int F11(int...);
    alias int F12(int, ...);
    static assert(is(DerivedFunctionType!(F10, F11) == void));
    static assert(is(DerivedFunctionType!(F10, F12) == void));
    static assert(is(DerivedFunctionType!(F11, F12) == void));

    // linkage equality
    alias extern(C) int F13(int);
    alias extern(D) int F14(int);
    alias extern(Windows) int F15(int);
    static assert(is(DerivedFunctionType!(F13, F14) == void));
    static assert(is(DerivedFunctionType!(F13, F15) == void));
    static assert(is(DerivedFunctionType!(F14, F15) == void));

    // ref & @property equality
    alias int F16(int);
    alias ref int F17(int);
    alias @property int F18(int);
    static assert(is(DerivedFunctionType!(F16, F17) == void));
    static assert(is(DerivedFunctionType!(F16, F18) == void));
    static assert(is(DerivedFunctionType!(F17, F18) == void));
}

package template staticIota(int beg, int end)
{
    static if (beg + 1 >= end)
    {
        static if (beg >= end)
        {
            alias staticIota = TypeTuple!();
        }
        else
        {
            alias staticIota = TypeTuple!(+beg);
        }
    }
    else
    {
        enum mid = beg + (end - beg) / 2;
        alias staticIota = TypeTuple!(staticIota!(beg, mid), staticIota!(mid, end));
    }
}

private template mixinAll(mixins...)
{
    static if (mixins.length == 1)
    {
        static if (is(typeof(mixins[0]) == string))
        {
            mixin(mixins[0]);
        }
        else
        {
            alias it = mixins[0];
            mixin it;
        }
    }
    else static if (mixins.length >= 2)
    {
        mixin mixinAll!(mixins[ 0 .. $/2]);
        mixin mixinAll!(mixins[$/2 .. $ ]);
    }
}

private template Bind(alias Template, args1...)
{
    alias Bind(args2...) = Template!(args1, args2);
}


/**
Options regarding auto-initialization of a $(D RefCounted) object (see
the definition of $(D RefCounted) below).
 */
enum RefCountedAutoInitialize
{
    /// Do not auto-initialize the object
    no,
    /// Auto-initialize the object
    yes,
}

/**
Defines a reference-counted object containing a $(D T) value as
payload. $(D RefCounted) keeps track of all references of an object,
and when the reference count goes down to zero, frees the underlying
store. $(D RefCounted) uses $(D malloc) and $(D free) for operation.

$(D RefCounted) is unsafe and should be used with care. No references
to the payload should be escaped outside the $(D RefCounted) object.

The $(D autoInit) option makes the object ensure the store is
automatically initialized. Leaving $(D autoInit ==
RefCountedAutoInitialize.yes) (the default option) is convenient but
has the cost of a test whenever the payload is accessed. If $(D
autoInit == RefCountedAutoInitialize.no), user code must call either
$(D refCountedStore.isInitialized) or $(D refCountedStore.ensureInitialized)
before attempting to access the payload. Not doing so results in null
pointer dereference.

Example:
----
// A pair of an $(D int) and a $(D size_t) - the latter being the
// reference count - will be dynamically allocated
auto rc1 = RefCounted!int(5);
assert(rc1 == 5);
// No more allocation, add just one extra reference count
auto rc2 = rc1;
// Reference semantics
rc2 = 42;
assert(rc1 == 42);
// the pair will be freed when rc1 and rc2 go out of scope
----
 */
struct RefCounted(T, RefCountedAutoInitialize autoInit =
        RefCountedAutoInitialize.yes)
if (!is(T == class))
{
    /// $(D RefCounted) storage implementation.
    struct RefCountedStore
    {
        private struct Impl
        {
            T _payload;
            size_t _count;
        }

        private Impl* _store;

        private void initialize(A...)(auto ref A args)
        {
            import core.memory : GC;
            import core.stdc.stdlib : malloc;
            import std.conv : emplace;
            import std.exception : enforce;

            _store = cast(Impl*) enforce(malloc(Impl.sizeof));
            static if (hasIndirections!T)
                GC.addRange(&_store._payload, T.sizeof);
            emplace(&_store._payload, args);
            _store._count = 1;
        }

        /**
           Returns $(D true) if and only if the underlying store has been
           allocated and initialized.
        */
        @property nothrow @safe
        bool isInitialized() const
        {
            return _store !is null;
        }

        /**
           Returns underlying reference count if it is allocated and initialized
           (a positive integer), and $(D 0) otherwise.
        */
        @property nothrow @safe
        size_t refCount() const
        {
            return isInitialized ? _store._count : 0;
        }

        /**
           Makes sure the payload was properly initialized. Such a
           call is typically inserted before using the payload.
        */
        void ensureInitialized()
        {
            if (!isInitialized) initialize();
        }

    }
    RefCountedStore _refCounted;

    /// Returns storage implementation struct.
    @property nothrow @safe
    ref inout(RefCountedStore) refCountedStore() inout
    {
        return _refCounted;
    }

/**
Constructor that initializes the payload.

Postcondition: $(D refCountedStore.isInitialized)
 */
    this(A...)(auto ref A args) if (A.length > 0)
    {
        _refCounted.initialize(args);
    }

/**
Constructor that tracks the reference count appropriately. If $(D
!refCountedStore.isInitialized), does nothing.
 */
    this(this)
    {
        if (!_refCounted.isInitialized) return;
        ++_refCounted._store._count;
    }

/**
Destructor that tracks the reference count appropriately. If $(D
!refCountedStore.isInitialized), does nothing. When the reference count goes
down to zero, calls $(D destroy) agaist the payload and calls $(D free)
to deallocate the corresponding resource.
 */
    ~this()
    {
        if (!_refCounted.isInitialized) return;
        assert(_refCounted._store._count > 0);
        if (--_refCounted._store._count)
            return;
        // Done, deallocate
        .destroy(_refCounted._store._payload);
        static if (hasIndirections!T)
        {
            import core.memory : GC;
            GC.removeRange(&_refCounted._store._payload);
        }
        import core.stdc.stdlib : free;
        free(_refCounted._store);
        _refCounted._store = null;
    }

/**
Assignment operators
 */
    void opAssign(typeof(this) rhs)
    {
        import std.algorithm : swap;

        swap(_refCounted._store, rhs._refCounted._store);
    }

/// Ditto
    void opAssign(T rhs)
    {
        import std.algorithm : move;

        static if (autoInit == RefCountedAutoInitialize.yes)
        {
            _refCounted.ensureInitialized();
        }
        else
        {
            assert(_refCounted.isInitialized);
        }
        move(rhs, _refCounted._store._payload);
    }

    //version to have a single properly ddoc'ed function (w/ correct sig)
    version(StdDdoc)
    {
        /**
        Returns a reference to the payload. If (autoInit ==
        RefCountedAutoInitialize.yes), calls $(D
        refCountedStore.ensureInitialized). Otherwise, just issues $(D
        assert(refCountedStore.isInitialized)). Used with $(D alias
        refCountedPayload this;), so callers can just use the $(D RefCounted)
        object as a $(D T).

        $(BLUE The first overload exists only if $(D autoInit == RefCountedAutoInitialize.yes).)
        So if $(D autoInit == RefCountedAutoInitialize.no)
        or called for a constant or immutable object, then
        $(D refCountedPayload) will also be qualified as safe and nothrow
        (but will still assert if not initialized).
         */
        @property
        ref T refCountedPayload();

        /// ditto
        @property nothrow @safe
        ref inout(T) refCountedPayload() inout;
    }
    else
    {
        static if (autoInit == RefCountedAutoInitialize.yes)
        {
            //Can't use inout here because of potential mutation
            @property
            ref T refCountedPayload()
            {
                _refCounted.ensureInitialized();
                return _refCounted._store._payload;
            }
        }

        @property nothrow @safe
        ref inout(T) refCountedPayload() inout
        {
            assert(_refCounted.isInitialized, "Attempted to access an uninitialized payload.");
            return _refCounted._store._payload;
        }
    }

/**
Returns a reference to the payload. If (autoInit ==
RefCountedAutoInitialize.yes), calls $(D
refCountedStore.ensureInitialized). Otherwise, just issues $(D
assert(refCountedStore.isInitialized)).
 */
    alias refCountedPayload this;
}

unittest
{
    RefCounted!int* p;
    {
        auto rc1 = RefCounted!int(5);
        p = &rc1;
        assert(rc1 == 5);
        assert(rc1._refCounted._store._count == 1);
        auto rc2 = rc1;
        assert(rc1._refCounted._store._count == 2);
        // Reference semantics
        rc2 = 42;
        assert(rc1 == 42);
        rc2 = rc2;
        assert(rc2._refCounted._store._count == 2);
        rc1 = rc2;
        assert(rc1._refCounted._store._count == 2);
    }
    assert(p._refCounted._store == null);

    // RefCounted as a member
    struct A
    {
        RefCounted!int x;
        this(int y)
        {
            x._refCounted.initialize(y);
        }
        A copy()
        {
            auto another = this;
            return another;
        }
    }
    auto a = A(4);
    auto b = a.copy();
    assert(a.x._refCounted._store._count == 2, "BUG 4356 still unfixed");
}

unittest
{
    import std.algorithm : swap;

    RefCounted!int p1, p2;
    swap(p1, p2);
}

// 6606
unittest
{
    union U {
       size_t i;
       void* p;
    }

    struct S {
       U u;
    }

    alias SRC = RefCounted!S;
}

// 6436
unittest
{
    struct S { this(ref int val) { assert(val == 3); ++val; } }

    int val = 3;
    auto s = RefCounted!S(val);
    assert(val == 4);
}

unittest
{
    RefCounted!int a;
    a = 5; //This should not assert
    assert(a == 5);

    RefCounted!int b;
    b = a; //This should not assert either
    assert(b == 5);
}

/**
Make proxy for $(D a).

Example:
----
struct MyInt
{
    private int value;
    mixin Proxy!value;

    this(int n){ value = n; }
}

MyInt n = 10;

// Enable operations that original type has.
++n;
assert(n == 11);
assert(n * 2 == 22);

void func(int n) { }

// Disable implicit conversions to original type.
//int x = n;
//func(n);
----
 */
mixin template Proxy(alias a)
{
    auto ref opEquals(this X, B)(auto ref B b)
    {
        static if (is(immutable B == immutable typeof(this)))
        {
            import std.algorithm;
            static assert(startsWith(a.stringof, "this."));
            return a == mixin("b."~a.stringof[5..$]);   // remove "this."
        }
        else
            return a == b;
    }

    auto ref opCmp(this X, B)(auto ref B b)
        if (!is(typeof(a.opCmp(b))) || !is(typeof(b.opCmp(a))))
    {
        static if (is(typeof(a.opCmp(b))))
            return a.opCmp(b);
        else static if (is(typeof(b.opCmp(a))))
            return -b.opCmp(a);
        else
            return a < b ? -1 : a > b ? +1 : 0;
    }

    auto ref opCall(this X, Args...)(auto ref Args args) { return a(args); }

    auto ref opCast(T, this X)() { return cast(T)a; }

    auto ref opIndex(this X, D...)(auto ref D i)               { return a[i]; }
    auto ref opSlice(this X      )()                           { return a[]; }
    auto ref opSlice(this X, B, E)(auto ref B b, auto ref E e) { return a[b..e]; }

    auto ref opUnary     (string op, this X      )()                           { return mixin(op~"a"); }
    auto ref opIndexUnary(string op, this X, D...)(auto ref D i)               { return mixin(op~"a[i]"); }
    auto ref opSliceUnary(string op, this X      )()                           { return mixin(op~"a[]"); }
    auto ref opSliceUnary(string op, this X, B, E)(auto ref B b, auto ref E e) { return mixin(op~"a[b..e]"); }

    auto ref opBinary(string op, this X, B)(auto ref B b)
    if (op == "in" && is(typeof(a in b)) || op != "in")
    {
        return mixin("a "~op~" b");
    }
    auto ref opBinaryRight(string op, this X, B)(auto ref B b) { return mixin("b "~op~" a"); }

    static if (!is(typeof(this) == class))
    {
        private import std.traits;
        static if (isAssignable!(typeof(a)))
        {
            auto ref opAssign(this X)(auto ref typeof(this) v)
            {
                a = mixin("v."~a.stringof[5..$]);   // remove "this."
                return this;
            }
        }
        else
        {
            @disable void opAssign(this X)(auto ref typeof(this) v);
        }
    }

    auto ref opAssign     (this X, V      )(auto ref V v) if (!is(V == typeof(this))) { return a       = v; }
    auto ref opIndexAssign(this X, V, D...)(auto ref V v, auto ref D i)               { return a[i]    = v; }
    auto ref opSliceAssign(this X, V      )(auto ref V v)                             { return a[]     = v; }
    auto ref opSliceAssign(this X, V, B, E)(auto ref V v, auto ref B b, auto ref E e) { return a[b..e] = v; }

    auto ref opOpAssign     (string op, this X, V      )(auto ref V v)                             { return mixin("a "      ~op~"= v"); }
    auto ref opIndexOpAssign(string op, this X, V, D...)(auto ref V v, auto ref D i)               { return mixin("a[i] "   ~op~"= v"); }
    auto ref opSliceOpAssign(string op, this X, V      )(auto ref V v)                             { return mixin("a[] "    ~op~"= v"); }
    auto ref opSliceOpAssign(string op, this X, V, B, E)(auto ref V v, auto ref B b, auto ref E e) { return mixin("a[b..e] "~op~"= v"); }

    template opDispatch(string name)
    {
        static if (is(typeof(__traits(getMember, a, name)) == function))
        {
            // non template function
            auto ref opDispatch(this X, Args...)(auto ref Args args) { return mixin("a."~name~"(args)"); }
        }
        else static if (is(typeof({ enum x = mixin("a."~name); })))
        {
            // built-in type field, manifest constant, and static non-mutable field
            enum opDispatch = mixin("a."~name);
        }
        else static if (is(typeof(mixin("a."~name))) || __traits(getOverloads, a, name).length != 0)
        {
            // field or property function
            @property auto ref opDispatch(this X)()                { return mixin("a."~name);        }
            @property auto ref opDispatch(this X, V)(auto ref V v) { return mixin("a."~name~" = v"); }
        }
        else
        {
            // member template
            template opDispatch(T...)
            {
                auto ref opDispatch(this X, Args...)(auto ref Args args){ return mixin("a."~name~"!T(args)"); }
            }
        }
    }

    static if (isArray!(typeof(a)))
    {
        auto opDollar() const { return a.length; }
    }
    else static if (is(typeof(a.opDollar!0)))
    {
        auto ref opDollar(size_t pos)() { return a.opDollar!pos(); }
    }
    else static if (is(typeof(a.opDollar) == function))
    {
        auto ref opDollar() { return a.opDollar(); }
    }
    else static if (is(typeof(a.opDollar)))
    {
        alias opDollar = a.opDollar;
    }
}
unittest
{
    static struct MyInt
    {
        private int value;
        mixin Proxy!value;
        this(int n) inout { value = n; }

        enum str = "str";
        static immutable arr = [1,2,3];
    }

    foreach (T; TypeTuple!(MyInt, const MyInt, immutable MyInt))
    {
        T m = 10;
        static assert(!__traits(compiles, { int x = m; }));
        static assert(!__traits(compiles, { void func(int n){} func(m); }));
        assert(m == 10);
        assert(m != 20);
        assert(m < 20);
        assert(+m == 10);
        assert(-m == -10);
        assert(cast(double)m == 10.0);
        assert(m + 10 == 20);
        assert(m - 5 == 5);
        assert(m * 20 == 200);
        assert(m / 2 == 5);
        assert(10 + m == 20);
        assert(15 - m == 5);
        assert(20 * m == 200);
        assert(50 / m == 5);
        static if (is(T == MyInt))  // mutable
        {
            assert(++m == 11);
            assert(m++ == 11); assert(m == 12);
            assert(--m == 11);
            assert(m-- == 11); assert(m == 10);
            m = m;
            m = 20; assert(m == 20);
        }
        static assert(T.max == int.max);
        static assert(T.min == int.min);
        static assert(T.init == int.init);
        static assert(T.str == "str");
        static assert(T.arr == [1,2,3]);
    }
}
unittest
{
    static struct MyArray
    {
        private int[] value;
        mixin Proxy!value;
        this(int[] arr) { value = arr; }
        this(immutable int[] arr) immutable { value = arr; }
    }

    foreach (T; TypeTuple!(MyArray, const MyArray, immutable MyArray))
    {
      static if (is(T == immutable) && !is(typeof({ T a = [1,2,3,4]; })))
        T a = [1,2,3,4].idup;   // workaround until qualified ctor is properly supported
      else
        T a = [1,2,3,4];
        assert(a == [1,2,3,4]);
        assert(a != [5,6,7,8]);
        assert(+a[0]    == 1);
        version (LittleEndian)
            assert(cast(ulong[])a == [0x0000_0002_0000_0001, 0x0000_0004_0000_0003]);
        else
            assert(cast(ulong[])a == [0x0000_0001_0000_0002, 0x0000_0003_0000_0004]);
        assert(a ~ [10,11] == [1,2,3,4,10,11]);
        assert(a[0]    == 1);
        assert(a[]     == [1,2,3,4]);
        assert(a[2..4] == [3,4]);
        static if (is(T == MyArray))    // mutable
        {
            a = a;
            a = [5,6,7,8];  assert(a == [5,6,7,8]);
            a[0]     = 0;   assert(a == [0,6,7,8]);
            a[]      = 1;   assert(a == [1,1,1,1]);
            a[0..3]  = 2;   assert(a == [2,2,2,1]);
            a[0]    += 2;   assert(a == [4,2,2,1]);
            a[]     *= 2;   assert(a == [8,4,4,2]);
            a[0..2] /= 2;   assert(a == [4,2,4,2]);
        }
    }
}
unittest
{
    class Foo
    {
        int field;

        @property const int val1(){ return field; }
        @property void val1(int n){ field = n; }

        @property ref int val2(){ return field; }

        const int func(int x, int y){ return x; }
        void func1(ref int a){ a = 9; }

        T opCast(T)(){ return T.init; }

        T tempfunc(T)() { return T.init; }
    }
    class Hoge
    {
        Foo foo;
        mixin Proxy!foo;
        this(Foo f) { foo = f; }
    }

    auto h = new Hoge(new Foo());
    int n;

    static assert(!__traits(compiles, { Foo f = h; }));

    // field
    h.field = 1;            // lhs of assign
    n = h.field;            // rhs of assign
    assert(h.field == 1);   // lhs of BinExp
    assert(1 == h.field);   // rhs of BinExp
    assert(n == 1);

    // getter/setter property function
    h.val1 = 4;
    n = h.val1;
    assert(h.val1 == 4);
    assert(4 == h.val1);
    assert(n == 4);

    // ref getter property function
    h.val2 = 8;
    n = h.val2;
    assert(h.val2 == 8);
    assert(8 == h.val2);
    assert(n == 8);

    // member function
    assert(h.func(2,4) == 2);
    h.func1(n);
    assert(n == 9);

    // bug5896 test
    assert(h.opCast!int() == 0);
    assert(cast(int)h == 0);
    const ih = new const Hoge(new Foo());
    static assert(!__traits(compiles, ih.opCast!int()));
    static assert(!__traits(compiles, cast(int)ih));

    // template member function
    assert(h.tempfunc!int() == 0);
}
unittest
{
    struct MyInt
    {
        int payload;

        mixin Proxy!payload;
    }

    MyInt v;
    v = v;

    struct Foo
    {
        @disable void opAssign(typeof(this));
    }
    struct MyFoo
    {
        Foo payload;

        mixin Proxy!payload;
    }
    MyFoo f;
    static assert(!__traits(compiles, f = f));

    struct MyFoo2
    {
        Foo payload;

        mixin Proxy!payload;

        // override default Proxy behavior
        void opAssign(typeof(this) rhs){}
    }
    MyFoo2 f2;
    f2 = f2;
}
unittest
{
    // bug8613
    static struct Name
    {
        mixin Proxy!val;
        private string val;
        this(string s) { val = s; }
    }

    bool[Name] names;
    names[Name("a")] = true;
    bool* b = Name("a") in names;
}

/**
Library typedef.
 */
alias Typedef(T) = .Typedef!(T, T.init);

/// ditto
struct Typedef(T, T init, string cookie=null)
{
    private T Typedef_payload = init;

    this(T init)
    {
        Typedef_payload = init;
    }

    mixin Proxy!Typedef_payload;
}

unittest
{
    Typedef!int x = 10;
    static assert(!__traits(compiles, { int y = x; }));
    static assert(!__traits(compiles, { long z = x; }));

    Typedef!int y = 10;
    assert(x == y);

    static assert(Typedef!int.init == int.init);

    Typedef!(float, 1.0) z; // specifies the init
    assert(z == 1.0);

    static assert(typeof(z).init == 1.0);

    alias Dollar = Typedef!(int, 0, "dollar");
    alias Yen    = Typedef!(int, 0, "yen");
    static assert(!is(Dollar == Yen));

    Typedef!(int[3]) sa;
    static assert(sa.length == 3);
    static assert(typeof(sa).length == 3);

    Typedef!(int[3]) dollar1;
    assert(dollar1[0..$] is dollar1[0..3]);

    Typedef!(int[]) dollar2;
    dollar2.length = 3;
    assert(dollar2[0..$] is dollar2[0..3]);

    static struct Dollar1
    {
        static struct DollarToken {}
        enum opDollar = DollarToken.init;
        auto opSlice(size_t, DollarToken) { return 1; }
        auto opSlice(size_t, size_t) { return 2; }
    }

    Typedef!Dollar1 drange1;
    assert(drange1[0..$] == 1);
    assert(drange1[0..1] == 2);

    static struct Dollar2
    {
        size_t opDollar(size_t pos)() { return pos == 0 ? 1 : 100; }
        size_t opIndex(size_t i, size_t j) { return i + j; }
    }

    Typedef!Dollar2 drange2;
    assert(drange2[$, $] == 101);

    static struct Dollar3
    {
        size_t opDollar() { return 123; }
        size_t opIndex(size_t i) { return i; }
    }

    Typedef!Dollar3 drange3;
    assert(drange3[$] == 123);
}

unittest
{
    // bug8655
    import std.typecons;
    import std.bitmanip;
    static import core.stdc.config;

    alias c_ulong = Typedef!(core.stdc.config.c_ulong);

    static struct Foo
    {
        mixin(bitfields!(
            c_ulong, "NameOffset", 31,
            c_ulong, "NameIsString", 1
        ));
    }
}


/**
Allocates a $(D class) object right inside the current scope,
therefore avoiding the overhead of $(D new). This facility is unsafe;
it is the responsibility of the user to not escape a reference to the
object outside the scope.

Note: it's illegal to move a class reference even if you are sure there
are no pointers to it. As such, it is illegal to move a scoped object.
 */
template scoped(T)
    if (is(T == class))
{
    // _d_newclass now use default GC alignment (looks like (void*).sizeof * 2 for
    // small objects). We will just use the maximum of filed alignments.
    alias alignment = classInstanceAlignment!T;
    alias aligned = _alignUp!alignment;

    static struct Scoped
    {
        // Addition of `alignment` is required as `Scoped_store` can be misaligned in memory.
        private void[aligned(__traits(classInstanceSize, T) + size_t.sizeof) + alignment] Scoped_store = void;

        @property inout(T) Scoped_payload() inout
        {
            void* alignedStore = cast(void*) aligned(cast(size_t) Scoped_store.ptr);
            // As `Scoped` can be unaligned moved in memory class instance should be moved accordingly.
            immutable size_t d = alignedStore - Scoped_store.ptr;
            size_t* currD = cast(size_t*) &Scoped_store[$ - size_t.sizeof];
            if(d != *currD)
            {
                import core.stdc.string;
                memmove(alignedStore, Scoped_store.ptr + *currD, __traits(classInstanceSize, T));
                *currD = d;
            }
            return cast(inout(T)) alignedStore;
        }
        alias Scoped_payload this;

        @disable this();
        @disable this(this);

        ~this()
        {
            // `destroy` will also write .init but we have no functions in druntime
            // for deterministic finalization and memory releasing for now.
            .destroy(Scoped_payload);
        }
    }

    /// Returns the scoped object
    @system auto scoped(Args...)(auto ref Args args)
    {
        import std.conv : emplace;

        Scoped result = void;
        void* alignedStore = cast(void*) aligned(cast(size_t) result.Scoped_store.ptr);
        immutable size_t d = alignedStore - result.Scoped_store.ptr;
        *cast(size_t*) &result.Scoped_store[$ - size_t.sizeof] = d;
        emplace!(Unqual!T)(result.Scoped_store[d .. $ - size_t.sizeof], args);
        return result;
    }
}
///
unittest
{
    class A
    {
        int x;
        this()     {x = 0;}
        this(int i){x = i;}
    }

    // Standard usage
    auto a1 = scoped!A();
    auto a2 = scoped!A(1);
    a1.x = 42;
    assert(a1.x == 42);
    assert(a2.x ==  1);

    // Restrictions
    static assert(!is(typeof({
        auto e1 = a1; // illegal, scoped objects can't be copied
        assert([a2][0].x == 42); // ditto
        alias ScopedObject = typeof(a1);
        auto e2 = ScopedObject();  //Illegal, must be built via scoped!A
        auto e3 = ScopedObject(1); //Illegal, must be built via scoped!A
    })));

    // Use as member variable
    struct B
    {
        typeof(scoped!A()) a; // note the trailing parentheses
    }

    // Use with alias
    alias makeScopedA = scoped!A;
    auto a6 = makeScopedA();
    auto a7 = makeScopedA();
}

private size_t _alignUp(size_t alignment)(size_t n)
    if(alignment > 0 && !((alignment - 1) & alignment))
{
    enum badEnd = alignment - 1; // 0b11, 0b111, ...
    return (n + badEnd) & ~badEnd;
}

unittest // Issue 6580 testcase
{
    enum alignment = (void*).alignof;

    static class C0 { }
    static class C1 { byte b; }
    static class C2 { byte[2] b; }
    static class C3 { byte[3] b; }
    static class C7 { byte[7] b; }
    static assert(scoped!C0().sizeof % alignment == 0);
    static assert(scoped!C1().sizeof % alignment == 0);
    static assert(scoped!C2().sizeof % alignment == 0);
    static assert(scoped!C3().sizeof % alignment == 0);
    static assert(scoped!C7().sizeof % alignment == 0);

    enum longAlignment = long.alignof;
    static class C1long
    {
        long long_; byte byte_ = 4;
        this() { }
        this(long _long, ref int i) { long_ = _long; ++i; }
    }
    static class C2long { byte[2] byte_ = [5, 6]; long long_ = 7; }
    static assert(scoped!C1long().sizeof % longAlignment == 0);
    static assert(scoped!C2long().sizeof % longAlignment == 0);

    void alignmentTest()
    {
        int var = 5;
        auto c1long = scoped!C1long(3, var);
        assert(var == 6);
        auto c2long = scoped!C2long();
        assert(cast(size_t)&c1long.long_ % longAlignment == 0);
        assert(cast(size_t)&c2long.long_ % longAlignment == 0);
        assert(c1long.long_ == 3 && c1long.byte_ == 4);
        assert(c2long.byte_ == [5, 6] && c2long.long_ == 7);
    }

    alignmentTest();

    version(DigitalMars)
    {
        void test(size_t size)
        {
            import core.stdc.stdlib;
            alloca(size);
            alignmentTest();
        }
        foreach(i; 0 .. 10)
            test(i);
    }
    else
    {
        void test(size_t size)()
        {
            byte[size] arr;
            alignmentTest();
        }
        foreach(i; TypeTuple!(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10))
            test!i();
    }
}

unittest // Original Issue 6580 testcase
{
    class C { int i; byte b; }

    auto sa = [scoped!C(), scoped!C()];
    assert(cast(size_t)&sa[0].i % int.alignof == 0);
    assert(cast(size_t)&sa[1].i % int.alignof == 0); // fails
}

unittest
{
    class A { int x = 1; }
    auto a1 = scoped!A();
    assert(a1.x == 1);
    auto a2 = scoped!A();
    a1.x = 42;
    a2.x = 53;
    assert(a1.x == 42);
}

unittest
{
    class A { int x = 1; this() { x = 2; } }
    auto a1 = scoped!A();
    assert(a1.x == 2);
    auto a2 = scoped!A();
    a1.x = 42;
    a2.x = 53;
    assert(a1.x == 42);
}

unittest
{
    class A { int x = 1; this(int y) { x = y; } ~this() {} }
    auto a1 = scoped!A(5);
    assert(a1.x == 5);
    auto a2 = scoped!A(42);
    a1.x = 42;
    a2.x = 53;
    assert(a1.x == 42);
}

unittest
{
    class A { static bool dead; ~this() { dead = true; } }
    class B : A { static bool dead; ~this() { dead = true; } }
    {
        auto b = scoped!B();
    }
    assert(B.dead, "asdasd");
    assert(A.dead, "asdasd");
}

unittest // Issue 8039 testcase
{
    static int dels;
    static struct S { ~this(){ ++dels; } }

    static class A { S s; }
    dels = 0; { scoped!A(); }
    assert(dels == 1);

    static class B { S[2] s; }
    dels = 0; { scoped!B(); }
    assert(dels == 2);

    static struct S2 { S[3] s; }
    static class C { S2[2] s; }
    dels = 0; { scoped!C(); }
    assert(dels == 6);

    static class D: A { S2[2] s; }
    dels = 0; { scoped!D(); }
    assert(dels == 1+6);
}

unittest
{
    // bug4500
    class A
    {
        this() { a = this; }
        this(int i) { a = this; }
        A a;
        bool check() { return this is a; }
    }

    auto a1 = scoped!A();
    assert(a1.check());

    auto a2 = scoped!A(1);
    assert(a2.check());

    a1.a = a1;
    assert(a1.check());
}

unittest
{
    static class A
    {
        static int sdtor;

        this() { ++sdtor; assert(sdtor == 1); }
        ~this() { assert(sdtor == 1); --sdtor; }
    }

    interface Bob {}

    static class ABob : A, Bob
    {
        this() { ++sdtor; assert(sdtor == 2); }
        ~this() { assert(sdtor == 2); --sdtor; }
    }

    A.sdtor = 0;
    scope(exit) assert(A.sdtor == 0);
    auto abob = scoped!ABob();
}

unittest
{
    static class A { this(int) {} }
    static assert(!__traits(compiles, scoped!A()));
}

unittest
{
    static class A { @property inout(int) foo() inout { return 1; } }

    auto a1 = scoped!A();
    assert(a1.foo == 1);
    static assert(is(typeof(a1.foo) == int));

    auto a2 = scoped!(const(A))();
    assert(a2.foo == 1);
    static assert(is(typeof(a2.foo) == const(int)));

    auto a3 = scoped!(immutable(A))();
    assert(a3.foo == 1);
    static assert(is(typeof(a3.foo) == immutable(int)));

    const c1 = scoped!A();
    assert(c1.foo == 1);
    static assert(is(typeof(c1.foo) == const(int)));

    const c2 = scoped!(const(A))();
    assert(c2.foo == 1);
    static assert(is(typeof(c2.foo) == const(int)));

    const c3 = scoped!(immutable(A))();
    assert(c3.foo == 1);
    static assert(is(typeof(c3.foo) == immutable(int)));
}

unittest
{
    class C { this(ref int val) { assert(val == 3); ++val; } }

    int val = 3;
    auto s = scoped!C(val);
    assert(val == 4);
}

unittest
{
    class C
    {
        this(){}
        this(int){}
        this(int, int){}
    }
    alias makeScopedC = scoped!C;

    auto a = makeScopedC();
    auto b = makeScopedC(1);
    auto c = makeScopedC(1, 1);

    static assert(is(typeof(a) == typeof(b)));
    static assert(is(typeof(b) == typeof(c)));
}

/**
Defines a simple, self-documenting yes/no flag. This makes it easy for
APIs to define functions accepting flags without resorting to $(D
bool), which is opaque in calls, and without needing to define an
enumerated type separately. Using $(D Flag!"Name") instead of $(D
bool) makes the flag's meaning visible in calls. Each yes/no flag has
its own type, which makes confusions and mix-ups impossible.

Example:
----
// Before
string getLine(bool keepTerminator)
{
    ...
    if (keepTerminator) ...
    ...
}
...
// Code calling getLine (usually far away from its definition) can't
// be understood without looking at the documentation, even by users
// familiar with the API. Assuming the reverse meaning
// (i.e. "ignoreTerminator") and inserting the wrong code compiles and
// runs with erroneous results.
auto line = getLine(false);

// After
string getLine(Flag!"KeepTerminator" keepTerminator)
{
    ...
    if (keepTerminator) ...
    ...
}
...
// Code calling getLine can be easily read and understood even by
// people not fluent with the API.
auto line = getLine(Flag!"KeepTerminator".yes);
----

Passing categorical data by means of unstructured $(D bool)
parameters is classified under "simple-data coupling" by Steve
McConnell in the $(LUCKY Code Complete) book, along with three other
kinds of coupling. The author argues citing several studies that
coupling has a negative effect on code quality. $(D Flag) offers a
simple structuring method for passing yes/no flags to APIs.

As a perk, the flag's name may be any string and as such can include
characters not normally allowed in identifiers, such as
spaces and dashes.
 */
template Flag(string name) {
    ///
    enum Flag : bool
    {
        /**
         When creating a value of type $(D Flag!"Name"), use $(D
         Flag!"Name".no) for the negative option. When using a value
         of type $(D Flag!"Name"), compare it against $(D
         Flag!"Name".no) or just $(D false) or $(D 0).  */
        no = false,

        /** When creating a value of type $(D Flag!"Name"), use $(D
         Flag!"Name".yes) for the affirmative option. When using a
         value of type $(D Flag!"Name"), compare it against $(D
         Flag!"Name".yes).
        */
        yes = true
    }
}

/**
Convenience names that allow using e.g. $(D Yes.encryption) instead of
$(D Flag!"encryption".yes) and $(D No.encryption) instead of $(D
Flag!"encryption".no).
*/
struct Yes
{
    template opDispatch(string name)
    {
        enum opDispatch = Flag!name.yes;
    }
}
//template yes(string name) { enum Flag!name yes = Flag!name.yes; }

/// Ditto
struct No
{
    template opDispatch(string name)
    {
        enum opDispatch = Flag!name.no;
    }
}
//template no(string name) { enum Flag!name no = Flag!name.no; }

unittest
{
    Flag!"abc" flag1;
    assert(flag1 == Flag!"abc".no);
    assert(flag1 == No.abc);
    assert(!flag1);
    if (flag1) assert(false);
    flag1 = Yes.abc;
    assert(flag1);
    if (!flag1) assert(false);
    if (flag1) {} else assert(false);
    assert(flag1 == Yes.abc);
}