• WhatMeWorry (27/27) Sep 19 2015 Does D provide complete template constraint granularity?
• Daniel Kozak (22/56) Sep 19 2015 http://dlang.org/expression.html#IsExpression
• WhatMeWorry (4/27) Sep 19 2015 Thanks! I keep going straight to std.traits and forget about the
• anonymous (9/35) Sep 19 2015 If the whole goal is to get how many members T has:

WhatMeWorry <kheaser gmail.com> writes:

Does D provide complete template constraint granularity?

In other words, I want to only accept structs in the template 
below.
I've find the isAggregateType which is close but no cigar. Am I 
missing
some other filters?

And a more open ended question.  Is there a more elegant solution 
for the
below function?  Maybe a one-liner?  I have a knack for making 
simple solutions
complex :)



// Calculate the number of components for openGL generic
// vertex attribute. Must be 1, 2, 3, 4.

// isAggregateType constraint accepts class, union, struct, and 
interface

int getNumberComponents(T)(T someStruct) if (isAggregateType!(T))
{
     int members = 0;
     foreach (i, member; someStruct.tupleof)
     {
         //writefln("Member %s:", i);
         //writefln("  type : %s", typeof(member).stringof);
         //writefln("  value: %s", member);
         members++;
     }
     return members;
}

Daniel Kozak <kozzi dlang.cz> writes:

WhatMeWorry p=C3=AD=C5=A1e v So 19. 09. 2015 v 17:09 +0000:
 Does D provide complete template constraint granularity?
=20
 In other words, I want to only accept structs in the template=20
 below.
 I've find the isAggregateType which is close but no cigar. Am I=20
 missing
 some other filters?
=20
 And a more open ended question.  Is there a more elegant solution=20
 for the
 below function?  Maybe a one-liner?  I have a knack for making=20
 simple solutions
 complex :)
=20
=20
=20
 // Calculate the number of components for openGL generic
 // vertex attribute. Must be 1, 2, 3, 4.
=20
 // isAggregateType constraint accepts class, union, struct, and=20
 interface
=20
 int getNumberComponents(T)(T someStruct) if (isAggregateType!(T))
 {
      int members =3D 0;
      foreach (i, member; someStruct.tupleof)
      {
          //writefln("Member %s:", i);
          //writefln("  type : %s", typeof(member).stringof);
          //writefln("  value: %s", member);
          members++;
      }
      return members;
 }

http://dlang.org/expression.html#IsExpression

3. is ( Type =3D=3D TypeSpecialization )

import std.stdio;

struct S
{
}

class C
{
}

void f(T)(T someStruct) if (is (T =3D=3D struct)) {
    writeln("struct");
}

void f(T)(T notStruct) if (!is(T =3D=3D struct)) {
    writeln("not a struct");
}

void main() {
    auto c =3D new C();
    auto s =3D S();

   f(c); // not a struct
   f(s); // struct
}

WhatMeWorry <kheaser gmail.com> writes:

On Saturday, 19 September 2015 at 17:18:23 UTC, Daniel Kozak 
wrote:
 WhatMeWorry píše v So 19. 09. 2015 v 17:09 +0000:
 [...]

 http://dlang.org/expression.html#IsExpression

 3. is ( Type == TypeSpecialization )

 import std.stdio;

 struct S
 {
 }

 class C
 {
 }

 void f(T)(T someStruct) if (is (T == struct)) {
     writeln("struct");
 }

 void f(T)(T notStruct) if (!is(T == struct)) {
     writeln("not a struct");
 }

 void main() {
     auto c = new C();
     auto s = S();

    f(c); // not a struct
    f(s); // struct
 }

Thanks!  I keep going straight to std.traits and forget about the 
is(Type)

anonymous <anonymous example.com> writes:

On Saturday 19 September 2015 19:09, WhatMeWorry wrote:

 And a more open ended question.  Is there a more elegant solution 
 for the
 below function?  Maybe a one-liner?  I have a knack for making 
 simple solutions
 complex :)
 
 
 
 // Calculate the number of components for openGL generic
 // vertex attribute. Must be 1, 2, 3, 4.
 
 // isAggregateType constraint accepts class, union, struct, and 
 interface
 
 int getNumberComponents(T)(T someStruct) if (isAggregateType!(T))
 {
      int members = 0;
      foreach (i, member; someStruct.tupleof)
      {
          //writefln("Member %s:", i);
          //writefln("  type : %s", typeof(member).stringof);
          //writefln("  value: %s", member);
          members++;
      }
      return members;
 }

If the whole goal is to get how many members T has:
----
template getNumberComponents(T) if (is(T == struct))
{
    enum getNumberComponents = T.tupleof.length;
}
----

Or you can write `T.tupleof.length` directly, of course.