digitalmars.D - ReturnType and overloaded functions

Yuxuan Shui (3/3) Jun 12 2015 When there are multiple overloaded functions, whose return type

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (18/21) Jun 12 2015 I am curious about the answer myself but there is the workaround of

ketmar (6/33) Jun 12 2015 or without importing `std.traits`:

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (3/34) Jun 12 2015 Good point. :) What is the difference of ReturnType then?

ketmar (4/19) Jun 13 2015 t));

Freddy (9/28) Jun 12 2015 Why not just use templates?

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (3/4) Jun 12 2015 The question is about overloaded functions.

Idan Arye (3/6) Jun 12 2015 The return type of the first declared one:

Kenji Hara via Digitalmars-d (7/14) Jun 12 2015 That's definitely a bug in current dmd. ReturnType should make error whe...

Yuxuan Shui (6/26) Jun 13 2015 It's kind of pointless to pick any one of the overloads. It would

Artur Skawina via Digitalmars-d (3/4) Jun 13 2015 alias ReturnType(alias F, A...) = typeof(F(A.init));

"Yuxuan Shui" <yshuiv7 gmail.com> writes:

When there are multiple overloaded functions, whose return type 
will I get when I use ReturnType? Is there a way I could choose a 
specific function by its parameter types?

Jun 12 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 06/12/2015 04:25 PM, Yuxuan Shui wrote:
 When there are multiple overloaded functions, whose return type will I
 get when I use ReturnType? Is there a way I could choose a specific
 function by its parameter types?

I am curious about the answer myself but there is the workaround of 
passing the overload through a lambda:

import std.traits;

int foo(long)
{
     return 0;
}

short foo(byte)
{
     return 0;
}

void main()
{
     static assert(is (ReturnType!(() => foo(long.init)) == int));
     static assert(is (ReturnType!(() => foo(byte.init)) == short));
}

Ali

Jun 12 2015

ketmar <ketmar ketmar.no-ip.org> writes:

On Fri, 12 Jun 2015 16:32:37 -0700, Ali =C3=87ehreli wrote:

 On 06/12/2015 04:25 PM, Yuxuan Shui wrote:
 When there are multiple overloaded functions, whose return type will I
 get when I use ReturnType? Is there a way I could choose a specific
 function by its parameter types?

=20
 I am curious about the answer myself but there is the workaround of
 passing the overload through a lambda:
=20
 import std.traits;
=20
 int foo(long)
 {
      return 0;
 }
=20
 short foo(byte)
 {
      return 0;
 }
=20
 void main()
 {
      static assert(is (ReturnType!(() =3D> foo(long.init)) =3D=3D int));
      static assert(is (ReturnType!(() =3D> foo(byte.init)) =3D=3D short))=

;
 }
=20
 Ali

or without importing `std.traits`:

  static assert(is(typeof(foo(long.init)) =3D=3D int));
  static assert(is(typeof(foo(byte.init)) =3D=3D short));
=

Jun 12 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 06/12/2015 05:04 PM, ketmar wrote:
 On Fri, 12 Jun 2015 16:32:37 -0700, Ali Çehreli wrote:

 On 06/12/2015 04:25 PM, Yuxuan Shui wrote:
 When there are multiple overloaded functions, whose return type will I
 get when I use ReturnType? Is there a way I could choose a specific
 function by its parameter types?

 I am curious about the answer myself but there is the workaround of
 passing the overload through a lambda:

 import std.traits;

 int foo(long)
 {
       return 0;
 }

 short foo(byte)
 {
       return 0;
 }

 void main()
 {
       static assert(is (ReturnType!(() => foo(long.init)) == int));
       static assert(is (ReturnType!(() => foo(byte.init)) == short));
 }

 Ali

 or without importing `std.traits`:

    static assert(is(typeof(foo(long.init)) == int));
    static assert(is(typeof(foo(byte.init)) == short));

Good point. :) What is the difference of ReturnType then?

Ali

Jun 12 2015

ketmar <ketmar ketmar.no-ip.org> writes:

On Fri, 12 Jun 2015 17:28:56 -0700, Ali =C3=87ehreli wrote:

 void main()
 {
       static assert(is (ReturnType!(() =3D> foo(long.init)) =3D=3D int)=



);
       static assert(is (ReturnType!(() =3D> foo(byte.init)) =3D=3D shor=



t));
 }

 Ali

 or without importing `std.traits`:

    static assert(is(typeof(foo(long.init)) =3D=3D int)); static
    assert(is(typeof(foo(byte.init)) =3D=3D short));

 Good point. :) What is the difference of ReturnType then?

i don't know. it looks nicer, maybe. ;-)=

Jun 13 2015

"Freddy" <Hexagonalstar64 gmail.com> writes:

 I am curious about the answer myself but there is the 
 workaround of passing the overload through a lambda:

 import std.traits;

 int foo(long)
 {
     return 0;
 }

 short foo(byte)
 {
     return 0;
 }

 void main()
 {
     static assert(is (ReturnType!(() => foo(long.init)) == 
 int));
     static assert(is (ReturnType!(() => foo(byte.init)) == 
 short));
 }

 Ali

Why not just use templates?

int foo(size_t id)() if(id == 0){
	return 0;
}

short foo(size_t id)() if(id == 1){
	return 0;
}

static assert(is(typeof(foo!0()) == int));
static assert(is(typeof(foo!1()) == short));

Jun 12 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 06/12/2015 06:44 PM, Freddy wrote:

 Why not just use templates?

The question is about overloaded functions.

Ali

Jun 12 2015

"Idan Arye" <GenericNPC gmail.com> writes:

On Friday, 12 June 2015 at 23:26:00 UTC, Yuxuan Shui wrote:
 When there are multiple overloaded functions, whose return type 
 will I get when I use ReturnType? Is there a way I could choose 
 a specific function by its parameter types?

The return type of the first declared one: 
http://dpaste.dzfl.pl/f448ec624592

Jun 12 2015

Kenji Hara via Digitalmars-d <digitalmars-d puremagic.com> writes:

2015-06-13 9:29 GMT+09:00 Idan Arye via Digitalmars-d <
digitalmars-d puremagic.com>:

 On Friday, 12 June 2015 at 23:26:00 UTC, Yuxuan Shui wrote:

 When there are multiple overloaded functions, whose return type will I
 get when I use ReturnType? Is there a way I could choose a specific
 function by its parameter types?

 The return type of the first declared one:
 http://dpaste.dzfl.pl/f448ec624592

That's definitely a bug in current dmd. ReturnType should make error when
overloaded function symbol is given.

To pick up one of the overloaded functions, you can use
__traits(getOverloads).

Kenji Hara

Jun 12 2015

"Yuxuan Shui" <yshuiv7 gmail.com> writes:

On Saturday, 13 June 2015 at 05:14:00 UTC, Kenji Hara wrote:
 2015-06-13 9:29 GMT+09:00 Idan Arye via Digitalmars-d <
 digitalmars-d puremagic.com>:

 On Friday, 12 June 2015 at 23:26:00 UTC, Yuxuan Shui wrote:

 When there are multiple overloaded functions, whose return 
 type will I
 get when I use ReturnType? Is there a way I could choose a 
 specific
 function by its parameter types?

 The return type of the first declared one:
 http://dpaste.dzfl.pl/f448ec624592

 That's definitely a bug in current dmd. ReturnType should make 
 error when
 overloaded function symbol is given.

 To pick up one of the overloaded functions, you can use
 __traits(getOverloads).

 Kenji Hara

It's kind of pointless to pick any one of the overloads. It would 
be convenient if a template exists to help us pick a overload by 
matching its parameter type.

That being said, the solution given earlier in this thread seems 
to work, I just wonder if there're any caveats.

Jun 13 2015

Artur Skawina via Digitalmars-d <digitalmars-d puremagic.com> writes:

On 06/13/15 01:25, Yuxuan Shui via Digitalmars-d wrote:
 When there are multiple overloaded functions, whose return type will I get
when I use ReturnType? Is there a way I could choose a specific function by its
parameter types?

   alias ReturnType(alias F, A...) = typeof(F(A.init));


artur

Jun 13 2015

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