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iteration.d
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iteration.d
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// Written in the D programming language.
/**
This is a submodule of $(MREF std, algorithm).
It contains generic iteration algorithms.
$(SCRIPT inhibitQuickIndex = 1;)
$(BOOKTABLE Cheat Sheet,
$(TR $(TH Function Name) $(TH Description))
$(T2 cache,
Eagerly evaluates and caches another range's `front`.)
$(T2 cacheBidirectional,
As above, but also provides `back` and `popBack`.)
$(T2 chunkBy,
`chunkBy!((a,b) => a[1] == b[1])([[1, 1], [1, 2], [2, 2], [2, 1]])`
returns a range containing 3 subranges: the first with just
`[1, 1]`; the second with the elements `[1, 2]` and `[2, 2]`;
and the third with just `[2, 1]`.)
$(T2 cumulativeFold,
`cumulativeFold!((a, b) => a + b)([1, 2, 3, 4])` returns a
lazily-evaluated range containing the successive reduced values `1`,
`3`, `6`, `10`.)
$(T2 each,
`each!writeln([1, 2, 3])` eagerly prints the numbers `1`, `2`
and `3` on their own lines.)
$(T2 filter,
`filter!(a => a > 0)([1, -1, 2, 0, -3])` iterates over elements `1`
and `2`.)
$(T2 filterBidirectional,
Similar to `filter`, but also provides `back` and `popBack` at
a small increase in cost.)
$(T2 fold,
`fold!((a, b) => a + b)([1, 2, 3, 4])` returns `10`.)
$(T2 group,
`group([5, 2, 2, 3, 3])` returns a range containing the tuples
`tuple(5, 1)`, `tuple(2, 2)`, and `tuple(3, 2)`.)
$(T2 joiner,
`joiner(["hello", "world!"], "; ")` returns a range that iterates
over the characters `"hello; world!"`. No new string is created -
the existing inputs are iterated.)
$(T2 map,
`map!(a => a * 2)([1, 2, 3])` lazily returns a range with the numbers
`2`, `4`, `6`.)
$(T2 mean,
Colloquially known as the average, `mean([1, 2, 3])` returns `2`.)
$(T2 permutations,
Lazily computes all permutations using Heap's algorithm.)
$(T2 reduce,
`reduce!((a, b) => a + b)([1, 2, 3, 4])` returns `10`.
This is the old implementation of `fold`.)
$(T2 splitter,
Lazily splits a range by a separator.)
$(T2 substitute,
`[1, 2].substitute(1, 0.1)` returns `[0.1, 2]`.)
$(T2 sum,
Same as `fold`, but specialized for accurate summation.)
$(T2 uniq,
Iterates over the unique elements in a range, which is assumed sorted.)
)
Copyright: Andrei Alexandrescu 2008-.
License: $(HTTP boost.org/LICENSE_1_0.txt, Boost License 1.0).
Authors: $(HTTP erdani.com, Andrei Alexandrescu)
Source: $(PHOBOSSRC std/algorithm/iteration.d)
Macros:
T2=$(TR $(TDNW $(LREF $1)) $(TD $+))
*/
module std.algorithm.iteration;
import std.functional : unaryFun, binaryFun;
import std.range.primitives;
import std.traits;
import std.typecons : Flag;
private template aggregate(fun...)
if (fun.length >= 1)
{
/* --Intentionally not ddoc--
* Aggregates elements in each subrange of the given range of ranges using
* the given aggregating function(s).
* Params:
* fun = One or more aggregating functions (binary functions that return a
* single _aggregate value of their arguments).
* ror = A range of ranges to be aggregated.
*
* Returns:
* A range representing the aggregated value(s) of each subrange
* of the original range. If only one aggregating function is specified,
* each element will be the aggregated value itself; if multiple functions
* are specified, each element will be a tuple of the aggregated values of
* each respective function.
*/
auto aggregate(RoR)(RoR ror)
if (isInputRange!RoR && isIterable!(ElementType!RoR))
{
return ror.map!(reduce!fun);
}
@safe unittest
{
import std.algorithm.comparison : equal, max, min;
auto data = [[4, 2, 1, 3], [4, 9, -1, 3, 2], [3]];
// Single aggregating function
auto agg1 = data.aggregate!max;
assert(agg1.equal([4, 9, 3]));
// Multiple aggregating functions
import std.typecons : tuple;
auto agg2 = data.aggregate!(max, min);
assert(agg2.equal([
tuple(4, 1),
tuple(9, -1),
tuple(3, 3)
]));
}
}
/++
`cache` eagerly evaluates $(REF_ALTTEXT front, front, std,range,primitives) of `range`
on each construction or call to $(REF_ALTTEXT popFront, popFront, std,range,primitives),
to store the result in a _cache.
The result is then directly returned when $(REF_ALTTEXT front, front, std,range,primitives) is called,
rather than re-evaluated.
This can be a useful function to place in a chain, after functions
that have expensive evaluation, as a lazy alternative to $(REF array, std,array).
In particular, it can be placed after a call to $(LREF map), or before a call
$(REF filter, std,range) or $(REF tee, std,range)
`cache` may provide
$(REF_ALTTEXT bidirectional range, isBidirectionalRange, std,range,primitives)
iteration if needed, but since this comes at an increased cost, it must be explicitly requested via the
call to `cacheBidirectional`. Furthermore, a bidirectional _cache will
evaluate the "center" element twice, when there is only one element left in
the range.
`cache` does not provide random access primitives,
as `cache` would be unable to _cache the random accesses.
If `Range` provides slicing primitives,
then `cache` will provide the same slicing primitives,
but `hasSlicing!Cache` will not yield true (as the $(REF hasSlicing, std,range,primitives)
trait also checks for random access).
Params:
range = an $(REF_ALTTEXT input range, isInputRange, std,range,primitives)
Returns:
An $(REF_ALTTEXT input range, isInputRange, std,range,primitives) with the cached values of range
+/
auto cache(Range)(Range range)
if (isInputRange!Range)
{
return _Cache!(Range, false)(range);
}
/// ditto
auto cacheBidirectional(Range)(Range range)
if (isBidirectionalRange!Range)
{
return _Cache!(Range, true)(range);
}
///
@safe unittest
{
import std.algorithm.comparison : equal;
import std.range, std.stdio;
import std.typecons : tuple;
ulong counter = 0;
double fun(int x)
{
++counter;
// http://en.wikipedia.org/wiki/Quartic_function
return ( (x + 4.0) * (x + 1.0) * (x - 1.0) * (x - 3.0) ) / 14.0 + 0.5;
}
// Without cache, with array (greedy)
auto result1 = iota(-4, 5).map!(a =>tuple(a, fun(a)))()
.filter!(a => a[1] < 0)()
.map!(a => a[0])()
.array();
// the values of x that have a negative y are:
assert(equal(result1, [-3, -2, 2]));
// Check how many times fun was evaluated.
// As many times as the number of items in both source and result.
assert(counter == iota(-4, 5).length + result1.length);
counter = 0;
// Without array, with cache (lazy)
auto result2 = iota(-4, 5).map!(a =>tuple(a, fun(a)))()
.cache()
.filter!(a => a[1] < 0)()
.map!(a => a[0])();
// the values of x that have a negative y are:
assert(equal(result2, [-3, -2, 2]));
// Check how many times fun was evaluated.
// Only as many times as the number of items in source.
assert(counter == iota(-4, 5).length);
}
// https://issues.dlang.org/show_bug.cgi?id=15891
@safe pure unittest
{
assert([1].map!(x=>[x].map!(y=>y)).cache.front.front == 1);
}
/++
Tip: `cache` is eager when evaluating elements. If calling front on the
underlying range has a side effect, it will be observable before calling
front on the actual cached range.
Furthermore, care should be taken composing `cache` with $(REF take, std,range).
By placing `take` before `cache`, then `cache` will be "aware"
of when the range ends, and correctly stop caching elements when needed.
If calling front has no side effect though, placing `take` after `cache`
may yield a faster range.
Either way, the resulting ranges will be equivalent, but maybe not at the
same cost or side effects.
+/
@safe unittest
{
import std.algorithm.comparison : equal;
import std.range;
int i = 0;
auto r = iota(0, 4).tee!((a){i = a;}, No.pipeOnPop);
auto r1 = r.take(3).cache();
auto r2 = r.cache().take(3);
assert(equal(r1, [0, 1, 2]));
assert(i == 2); //The last "seen" element was 2. The data in cache has been cleared.
assert(equal(r2, [0, 1, 2]));
assert(i == 3); //cache has accessed 3. It is still stored internally by cache.
}
@safe unittest
{
import std.algorithm.comparison : equal;
import std.range;
auto a = [1, 2, 3, 4];
assert(equal(a.map!(a => (a - 1) * a)().cache(), [ 0, 2, 6, 12]));
assert(equal(a.map!(a => (a - 1) * a)().cacheBidirectional().retro(), [12, 6, 2, 0]));
auto r1 = [1, 2, 3, 4].cache() [1 .. $];
auto r2 = [1, 2, 3, 4].cacheBidirectional()[1 .. $];
assert(equal(r1, [2, 3, 4]));
assert(equal(r2, [2, 3, 4]));
}
@safe unittest
{
import std.algorithm.comparison : equal;
//immutable test
static struct S
{
int i;
this(int i)
{
//this.i = i;
}
}
immutable(S)[] s = [S(1), S(2), S(3)];
assert(equal(s.cache(), s));
assert(equal(s.cacheBidirectional(), s));
}
@safe pure nothrow unittest
{
import std.algorithm.comparison : equal;
//safety etc
auto a = [1, 2, 3, 4];
assert(equal(a.cache(), a));
assert(equal(a.cacheBidirectional(), a));
}
@safe unittest
{
char[][] stringbufs = ["hello".dup, "world".dup];
auto strings = stringbufs.map!((a)=>a.idup)().cache();
assert(strings.front is strings.front);
}
@safe unittest
{
import std.range : cycle;
import std.algorithm.comparison : equal;
auto c = [1, 2, 3].cycle().cache();
c = c[1 .. $];
auto d = c[0 .. 1];
assert(d.equal([2]));
}
@safe unittest
{
static struct Range
{
bool initialized = false;
bool front() @property {return initialized = true;}
void popFront() {initialized = false;}
enum empty = false;
}
auto r = Range().cache();
assert(r.source.initialized == true);
}
private struct _Cache(R, bool bidir)
{
import core.exception : RangeError;
private
{
import std.algorithm.internal : algoFormat;
import std.meta : AliasSeq;
alias E = ElementType!R;
alias UE = Unqual!E;
R source;
static if (bidir) alias CacheTypes = AliasSeq!(UE, UE);
else alias CacheTypes = AliasSeq!UE;
CacheTypes caches;
static assert(isAssignable!(UE, E) && is(UE : E),
algoFormat(
"Cannot instantiate range with %s because %s elements are not assignable to %s.",
R.stringof,
E.stringof,
UE.stringof
)
);
}
this(R range)
{
source = range;
if (!range.empty)
{
caches[0] = source.front;
static if (bidir)
caches[1] = source.back;
}
else
{
// needed, because the compiler cannot deduce, that 'caches' is initialized
// see https://issues.dlang.org/show_bug.cgi?id=15891
caches[0] = UE.init;
static if (bidir)
caches[1] = UE.init;
}
}
static if (isInfinite!R)
enum empty = false;
else
bool empty() @property
{
return source.empty;
}
static if (hasLength!R) auto length() @property
{
return source.length;
}
E front() @property
{
version (assert) if (empty) throw new RangeError();
return caches[0];
}
static if (bidir) E back() @property
{
version (assert) if (empty) throw new RangeError();
return caches[1];
}
void popFront()
{
version (assert) if (empty) throw new RangeError();
source.popFront();
if (!source.empty)
caches[0] = source.front;
else
{
// see https://issues.dlang.org/show_bug.cgi?id=15891
caches[0] = UE.init;
static if (bidir)
caches[1] = UE.init;
}
}
static if (bidir) void popBack()
{
version (assert) if (empty) throw new RangeError();
source.popBack();
if (!source.empty)
caches[1] = source.back;
else
{
// see https://issues.dlang.org/show_bug.cgi?id=15891
caches[0] = UE.init;
caches[1] = UE.init;
}
}
static if (isForwardRange!R)
{
private this(R source, ref CacheTypes caches)
{
this.source = source;
this.caches = caches;
}
typeof(this) save() @property
{
return typeof(this)(source.save, caches);
}
}
static if (hasSlicing!R)
{
enum hasEndSlicing = is(typeof(source[size_t.max .. $]));
static if (hasEndSlicing)
{
private static struct DollarToken{}
enum opDollar = DollarToken.init;
auto opSlice(size_t low, DollarToken)
{
return typeof(this)(source[low .. $]);
}
}
static if (!isInfinite!R)
{
typeof(this) opSlice(size_t low, size_t high)
{
return typeof(this)(source[low .. high]);
}
}
else static if (hasEndSlicing)
{
auto opSlice(size_t low, size_t high)
in
{
assert(low <= high, "Bounds error when slicing cache.");
}
do
{
import std.range : takeExactly;
return this[low .. $].takeExactly(high - low);
}
}
}
}
/**
Implements the homonym function (also known as `transform`) present
in many languages of functional flavor. The call `map!(fun)(range)`
returns a range of which elements are obtained by applying `fun(a)`
left to right for all elements `a` in `range`. The original ranges are
not changed. Evaluation is done lazily.
Params:
fun = one or more transformation functions
See_Also:
$(HTTP en.wikipedia.org/wiki/Map_(higher-order_function), Map (higher-order function))
*/
template map(fun...)
if (fun.length >= 1)
{
/**
Params:
r = an $(REF_ALTTEXT input range, isInputRange, std,range,primitives)
Returns:
A range with each fun applied to all the elements. If there is more than one
fun, the element type will be `Tuple` containing one element for each fun.
*/
auto map(Range)(Range r) if (isInputRange!(Unqual!Range))
{
import std.meta : AliasSeq, staticMap;
alias RE = ElementType!(Range);
static if (fun.length > 1)
{
import std.functional : adjoin;
import std.meta : staticIndexOf;
alias _funs = staticMap!(unaryFun, fun);
alias _fun = adjoin!_funs;
// Once https://issues.dlang.org/show_bug.cgi?id=5710 is fixed
// accross all compilers (as of 2020-04, it wasn't fixed in LDC and GDC),
// this validation loop can be moved into a template.
foreach (f; _funs)
{
static assert(!is(typeof(f(RE.init)) == void),
"Mapping function(s) must not return void: " ~ _funs.stringof);
}
}
else
{
alias _fun = unaryFun!fun;
alias _funs = AliasSeq!(_fun);
// Do the validation separately for single parameters due to
// https://issues.dlang.org/show_bug.cgi?id=15777.
static assert(!is(typeof(_fun(RE.init)) == void),
"Mapping function(s) must not return void: " ~ _funs.stringof);
}
return MapResult!(_fun, Range)(r);
}
}
///
@safe @nogc unittest
{
import std.algorithm.comparison : equal;
import std.range : chain, only;
auto squares =
chain(only(1, 2, 3, 4), only(5, 6)).map!(a => a * a);
assert(equal(squares, only(1, 4, 9, 16, 25, 36)));
}
/**
Multiple functions can be passed to `map`. In that case, the
element type of `map` is a tuple containing one element for each
function.
*/
@safe unittest
{
auto sums = [2, 4, 6, 8];
auto products = [1, 4, 9, 16];
size_t i = 0;
foreach (result; [ 1, 2, 3, 4 ].map!("a + a", "a * a"))
{
assert(result[0] == sums[i]);
assert(result[1] == products[i]);
++i;
}
}
/**
You may alias `map` with some function(s) to a symbol and use
it separately:
*/
@safe unittest
{
import std.algorithm.comparison : equal;
import std.conv : to;
alias stringize = map!(to!string);
assert(equal(stringize([ 1, 2, 3, 4 ]), [ "1", "2", "3", "4" ]));
}
// Verify workaround for https://issues.dlang.org/show_bug.cgi?id=15777
@safe unittest
{
import std.algorithm.mutation, std.string;
auto foo(string[] args)
{
return args.map!strip;
}
}
private struct MapResult(alias fun, Range)
{
alias R = Unqual!Range;
R _input;
static if (isBidirectionalRange!R)
{
@property auto ref back()()
{
assert(!empty, "Attempting to fetch the back of an empty map.");
return fun(_input.back);
}
void popBack()()
{
assert(!empty, "Attempting to popBack an empty map.");
_input.popBack();
}
}
this(R input)
{
_input = input;
}
static if (isInfinite!R)
{
// Propagate infinite-ness.
enum bool empty = false;
}
else
{
@property bool empty()
{
return _input.empty;
}
}
void popFront()
{
assert(!empty, "Attempting to popFront an empty map.");
_input.popFront();
}
@property auto ref front()
{
assert(!empty, "Attempting to fetch the front of an empty map.");
return fun(_input.front);
}
static if (isRandomAccessRange!R)
{
static if (is(typeof(Range.init[ulong.max])))
private alias opIndex_t = ulong;
else
private alias opIndex_t = uint;
auto ref opIndex(opIndex_t index)
{
return fun(_input[index]);
}
}
static if (hasLength!R)
{
@property auto length()
{
return _input.length;
}
alias opDollar = length;
}
static if (hasSlicing!R)
{
static if (is(typeof(_input[ulong.max .. ulong.max])))
private alias opSlice_t = ulong;
else
private alias opSlice_t = uint;
static if (hasLength!R)
{
auto opSlice(opSlice_t low, opSlice_t high)
{
return typeof(this)(_input[low .. high]);
}
}
else static if (is(typeof(_input[opSlice_t.max .. $])))
{
struct DollarToken{}
enum opDollar = DollarToken.init;
auto opSlice(opSlice_t low, DollarToken)
{
return typeof(this)(_input[low .. $]);
}
auto opSlice(opSlice_t low, opSlice_t high)
{
import std.range : takeExactly;
return this[low .. $].takeExactly(high - low);
}
}
}
static if (isForwardRange!R)
{
@property auto save()
{
return typeof(this)(_input.save);
}
}
}
@safe unittest
{
import std.algorithm.comparison : equal;
import std.conv : to;
import std.functional : adjoin;
alias stringize = map!(to!string);
assert(equal(stringize([ 1, 2, 3, 4 ]), [ "1", "2", "3", "4" ]));
uint counter;
alias count = map!((a) { return counter++; });
assert(equal(count([ 10, 2, 30, 4 ]), [ 0, 1, 2, 3 ]));
counter = 0;
adjoin!((a) { return counter++; }, (a) { return counter++; })(1);
alias countAndSquare = map!((a) { return counter++; }, (a) { return counter++; });
//assert(equal(countAndSquare([ 10, 2 ]), [ tuple(0u, 100), tuple(1u, 4) ]));
}
@safe unittest
{
import std.algorithm.comparison : equal;
import std.ascii : toUpper;
import std.internal.test.dummyrange;
import std.range;
import std.typecons : tuple;
import std.random : uniform, Random = Xorshift;
int[] arr1 = [ 1, 2, 3, 4 ];
const int[] arr1Const = arr1;
int[] arr2 = [ 5, 6 ];
auto squares = map!("a * a")(arr1Const);
assert(squares[$ - 1] == 16);
assert(equal(squares, [ 1, 4, 9, 16 ][]));
assert(equal(map!("a * a")(chain(arr1, arr2)), [ 1, 4, 9, 16, 25, 36 ][]));
// Test the caching stuff.
assert(squares.back == 16);
auto squares2 = squares.save;
assert(squares2.back == 16);
assert(squares2.front == 1);
squares2.popFront();
assert(squares2.front == 4);
squares2.popBack();
assert(squares2.front == 4);
assert(squares2.back == 9);
assert(equal(map!("a * a")(chain(arr1, arr2)), [ 1, 4, 9, 16, 25, 36 ][]));
uint i;
foreach (e; map!("a", "a * a")(arr1))
{
assert(e[0] == ++i);
assert(e[1] == i * i);
}
// Test length.
assert(squares.length == 4);
assert(map!"a * a"(chain(arr1, arr2)).length == 6);
// Test indexing.
assert(squares[0] == 1);
assert(squares[1] == 4);
assert(squares[2] == 9);
assert(squares[3] == 16);
// Test slicing.
auto squareSlice = squares[1 .. squares.length - 1];
assert(equal(squareSlice, [4, 9][]));
assert(squareSlice.back == 9);
assert(squareSlice[1] == 9);
// Test on a forward range to make sure it compiles when all the fancy
// stuff is disabled.
auto fibsSquares = map!"a * a"(recurrence!("a[n-1] + a[n-2]")(1, 1));
assert(fibsSquares.front == 1);
fibsSquares.popFront();
fibsSquares.popFront();
assert(fibsSquares.front == 4);
fibsSquares.popFront();
assert(fibsSquares.front == 9);
auto repeatMap = map!"a"(repeat(1));
auto gen = Random(123_456_789);
auto index = uniform(0, 1024, gen);
static assert(isInfinite!(typeof(repeatMap)));
assert(repeatMap[index] == 1);
auto intRange = map!"a"([1,2,3]);
static assert(isRandomAccessRange!(typeof(intRange)));
assert(equal(intRange, [1, 2, 3]));
foreach (DummyType; AllDummyRanges)
{
DummyType d;
auto m = map!"a * a"(d);
static assert(propagatesRangeType!(typeof(m), DummyType));
assert(equal(m, [1,4,9,16,25,36,49,64,81,100]));
}
//Test string access
string s1 = "hello world!";
dstring s2 = "日本語";
dstring s3 = "hello world!"d;
auto ms1 = map!(std.ascii.toUpper)(s1);
auto ms2 = map!(std.ascii.toUpper)(s2);
auto ms3 = map!(std.ascii.toUpper)(s3);
static assert(!is(ms1[0])); //narrow strings can't be indexed
assert(ms2[0] == '日');
assert(ms3[0] == 'H');
static assert(!is(ms1[0 .. 1])); //narrow strings can't be sliced
assert(equal(ms2[0 .. 2], "日本"w));
assert(equal(ms3[0 .. 2], "HE"));
// https://issues.dlang.org/show_bug.cgi?id=5753
static void voidFun(int) {}
static int nonvoidFun(int) { return 0; }
static assert(!__traits(compiles, map!voidFun([1])));
static assert(!__traits(compiles, map!(voidFun, voidFun)([1])));
static assert(!__traits(compiles, map!(nonvoidFun, voidFun)([1])));
static assert(!__traits(compiles, map!(voidFun, nonvoidFun)([1])));
static assert(!__traits(compiles, map!(a => voidFun(a))([1])));
// https://issues.dlang.org/show_bug.cgi?id=15480
auto dd = map!(z => z * z, c => c * c * c)([ 1, 2, 3, 4 ]);
assert(dd[0] == tuple(1, 1));
assert(dd[1] == tuple(4, 8));
assert(dd[2] == tuple(9, 27));
assert(dd[3] == tuple(16, 64));
assert(dd.length == 4);
}
@safe unittest
{
import std.algorithm.comparison : equal;
import std.range;
auto LL = iota(1L, 4L);
auto m = map!"a*a"(LL);
assert(equal(m, [1L, 4L, 9L]));
}
@safe unittest
{
import std.range : iota;
// https://issues.dlang.org/show_bug.cgi?id=10130 - map of iota with const step.
const step = 2;
assert(map!(i => i)(iota(0, 10, step)).walkLength == 5);
// Need these to all by const to repro the float case, due to the
// CommonType template used in the float specialization of iota.
const floatBegin = 0.0;
const floatEnd = 1.0;
const floatStep = 0.02;
assert(map!(i => i)(iota(floatBegin, floatEnd, floatStep)).walkLength == 50);
}
@safe unittest
{
import std.algorithm.comparison : equal;
import std.range;
//slicing infinites
auto rr = iota(0, 5).cycle().map!"a * a"();
alias RR = typeof(rr);
static assert(hasSlicing!RR);
rr = rr[6 .. $]; //Advances 1 cycle and 1 unit
assert(equal(rr[0 .. 5], [1, 4, 9, 16, 0]));
}
@safe unittest
{
import std.range;
struct S {int* p;}
auto m = immutable(S).init.repeat().map!"a".save;
assert(m.front == immutable(S)(null));
}
// Issue 20928
@safe unittest
{
struct Always3
{
enum empty = false;
auto save() { return this; }
long front() { return 3; }
void popFront() {}
long opIndex(ulong i) { return 3; }
long opIndex(ulong i) immutable { return 3; }
}
import std.algorithm.iteration : map;
Always3.init.map!(e => e)[ulong.max];
}
// each
/**
Eagerly iterates over `r` and calls `fun` over _each element.
If no function to call is specified, `each` defaults to doing nothing but
consuming the entire range. `r.front` will be evaluated, but that can be avoided
by specifying a lambda with a `lazy` parameter.
`each` also supports `opApply`-based types, so it works with e.g. $(REF
parallel, std,parallelism).
Normally the entire range is iterated. If partial iteration (early stopping) is
desired, `fun` needs to return a value of type $(REF Flag,
std,typecons)`!"each"` (`Yes.each` to continue iteration, or `No.each` to stop
iteration).
Params:
fun = function to apply to _each element of the range
r = range or iterable over which `each` iterates
Returns: `Yes.each` if the entire range was iterated, `No.each` in case of early
stopping.
See_Also: $(REF tee, std,range)
*/
template each(alias fun = "a")
{
import std.meta : AliasSeq;
import std.traits : Parameters;
import std.typecons : Flag, Yes, No;
private:
alias BinaryArgs = AliasSeq!(fun, "i", "a");
enum isRangeUnaryIterable(R) =
is(typeof(unaryFun!fun(R.init.front)));
enum isRangeBinaryIterable(R) =
is(typeof(binaryFun!BinaryArgs(0, R.init.front)));
enum isRangeIterable(R) =
isInputRange!R &&
(isRangeUnaryIterable!R || isRangeBinaryIterable!R);
enum isForeachUnaryIterable(R) =
is(typeof((R r) {
foreach (ref a; r)
cast(void) unaryFun!fun(a);
}));
enum isForeachUnaryWithIndexIterable(R) =
is(typeof((R r) {
foreach (i, ref a; r)
cast(void) binaryFun!BinaryArgs(i, a);
}));
enum isForeachBinaryIterable(R) =
is(typeof((R r) {
foreach (ref a, ref b; r)
cast(void) binaryFun!fun(a, b);
}));
enum isForeachIterable(R) =
(!isForwardRange!R || isDynamicArray!R) &&
(isForeachUnaryIterable!R || isForeachBinaryIterable!R ||
isForeachUnaryWithIndexIterable!R);
public:
/**
Params:
r = range or iterable over which each iterates
*/
Flag!"each" each(Range)(Range r)
if (!isForeachIterable!Range && (
isRangeIterable!Range ||
__traits(compiles, typeof(r.front).length)))
{
static if (isRangeIterable!Range)
{
debug(each) pragma(msg, "Using while for ", Range.stringof);
static if (isRangeUnaryIterable!Range)
{
while (!r.empty)
{
static if (!is(typeof(unaryFun!fun(r.front)) == Flag!"each"))
{
cast(void) unaryFun!fun(r.front);
}
else
{
if (unaryFun!fun(r.front) == No.each) return No.each;
}
r.popFront();
}
}
else // if (isRangeBinaryIterable!Range)
{
size_t i = 0;
while (!r.empty)
{
static if (!is(typeof(binaryFun!BinaryArgs(i, r.front)) == Flag!"each"))
{
cast(void) binaryFun!BinaryArgs(i, r.front);
}
else
{
if (binaryFun!BinaryArgs(i, r.front) == No.each) return No.each;
}
r.popFront();
i++;