uniform initialization for type tuples too

[dlangBugzillaToGithub]

monarchdodra reported this on 2014-04-06T12:14:28Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=12530

CC List

• Nick Treleaven (@ntrel)

Description

Not sure if enhancement request or bug, but filing as EH.

I think these should work:

//----
    auto a = TypeTuple!(int, int, int)();� //(0, 0, 0)
    auto b = TypeTuple!(int, int, int)(1); //(1, 1, 1)
    //auto c = TypeTuple!(int, int, int)(1, 2);� //Should fail
    auto d = TypeTuple!(int, int, int)(1, 2, 3); //(1, 2, 3)
//----

Currently they all produce:
Error: function expected before (), not (int, int, int) of type (int, int, int)

In particular, I think this should work:
//----
    TypeTuple!(int, int, int) a = ...;
    TypeTuple!(int, int, int) b = TypeTuple!(int, int, int)(a);
//----
Though arguably, it's the exactly the same as the "d" case above.

[dlangBugzillaToGithub]

bearophile_hugs commented on 2014-04-06T12:32:55Z

(In reply to comment #0)

> I think these should work:
> 
>     auto a = TypeTuple!(int, int, int)();� //(0, 0, 0)
>     auto b = TypeTuple!(int, int, int)(1); //(1, 1, 1)
>     //auto c = TypeTuple!(int, int, int)(1, 2);� //Should fail
>     auto d = TypeTuple!(int, int, int)(1, 2, 3); //(1, 2, 3)

Please show one or more use cases.

[dlangBugzillaToGithub]

monarchdodra commented on 2014-04-06T13:02:13Z

(In reply to comment #1)
> Please show one or more use cases.

I've had need of this, for example, to transform the types of variadic arguments, before passing them to another function. "reduce" or "uninitializedArray" come to mind:

//----
void main()
{
    uninitialized!(int[][])(1, 2);
}

alias ToSizeT(T) = size_t;
enum  IsSizeT(T) = is(S == size_t);

auto uninitialized(T, Args...)(Args args)
{
    //transform the "int" inference to "size_t"
    alias SizeTArgs = staticMap!(ToSizeT, Args);

    //Call with the same arguments, but cast to size_t...
    //if the cast is implicitly safe
    return impl!T(SizeTArgs(args));
}

auto impl(T, Args...)(Args args) //Avoid bloat by requesting size_t args.
{
    static assert(allSatisfy!(IsSizeT, Args));
}
//----

The same design can be used to transform/forward args, say to unqualify all of them at once:
//----
void myFun(Args(Args args))
{
    alias UArgs = staticMap!(Unqual, Args);
    static if (!is(UArgs == ARgs))
        myFun(UArgs(args));
    else
    {
        //actual implementation here
    }
}

Or, in the case of reduce, to build the different seeds from front:
auto result = tuple(SeedTypes(r.front));

[dlangBugzillaToGithub]

nick (@ntrel) commented on 2024-08-23T16:47:24Z

>    auto b = TypeTuple!(int, int, int)(1); //(1, 1, 1)
...
>    TypeTuple!(int, int, int) a = ...;
>    TypeTuple!(int, int, int) b = TypeTuple!(int, int, int)(a);

Not uniform initialization, but you can do:

import std.meta: AliasSeq;

AliasSeq!(int, int, int) vs = 1;
assert(vs == AliasSeq!(1, 1, 1));

AliasSeq!(int, int, int) xs = vs;