• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (47/47) Oct 29 2013 Template mixins can take scope names to resolve name conflicts:
• John Colvin (15/65) Oct 30 2013 This is a good workaround that I commonly use. Should be in

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

Template mixins can take scope names to resolve name conflicts:

   http://dlang.org/template-mixin.html

import std.stdio;

template Templ()
{
     int i;
}

void main()
{
     mixin Templ!();
     mixin Templ!();

     writeln(i);
     /* Error: deneme.main.Templ!().i at deneme.d(149327)
      * conflicts with deneme.main.Templ!().i at
      * deneme.d(149327) */
}

The solution is to use mixin identifiers:

     mixin Templ!() A;
     mixin Templ!() B;

The code compiles but of course one must specify which 'i' to use:

     writeln(A.i);

The same feature does not exist for string mixins:

   http://dlang.org/mixin.html

Is there a reason for the omission? Is there an enhancement request for it?

However, the workaround is surprisingly trivial. First, the problem:

import std.stdio;

void main()
{
     mixin ("int i;");
     mixin ("int i;");

     writeln(i);
     /* Error: declaration deneme.main.i is already defined */
}

The solution:

import std.stdio;

template TemplateMixinize(string Str)
{
     mixin (Str);
}

void main()
{
     mixin TemplateMixinize!("int i;") A;
     mixin TemplateMixinize!("int i;") B;

     writeln(A.i);
}

Does TemplateMixinize :p already exist in Phobos?

Ali

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Tuesday, 29 October 2013 at 23:16:46 UTC, Ali Çehreli wrote:
 Template mixins can take scope names to resolve name conflicts:

   http://dlang.org/template-mixin.html

 import std.stdio;

 template Templ()
 {
     int i;
 }

 void main()
 {
     mixin Templ!();
     mixin Templ!();

     writeln(i);
     /* Error: deneme.main.Templ!().i at deneme.d(149327)
      * conflicts with deneme.main.Templ!().i at
      * deneme.d(149327) */
 }

 The solution is to use mixin identifiers:

     mixin Templ!() A;
     mixin Templ!() B;

 The code compiles but of course one must specify which 'i' to 
 use:

     writeln(A.i);

 The same feature does not exist for string mixins:

   http://dlang.org/mixin.html

 Is there a reason for the omission? Is there an enhancement 
 request for it?

 However, the workaround is surprisingly trivial. First, the 
 problem:

 import std.stdio;

 void main()
 {
     mixin ("int i;");
     mixin ("int i;");

     writeln(i);
     /* Error: declaration deneme.main.i is already defined */
 }

 The solution:

 import std.stdio;

 template TemplateMixinize(string Str)
 {
     mixin (Str);
 }

 void main()
 {
     mixin TemplateMixinize!("int i;") A;
     mixin TemplateMixinize!("int i;") B;

     writeln(A.i);
 }

 Does TemplateMixinize :p already exist in Phobos?

 Ali

This is a good workaround that I commonly use. Should be in 
phobos.

However, the real problem is the opposite one: To use a mixin 
template without it having it's own scope.
Having to resort to string mixins to add constructors or do 
proper overloads is ugly and can cause a code duplication (one 
mixin template and one string template) which is exactly what 
mixins are for avoiding.

Perhaps we could have:

mixin template MixinTemplate(...){...}

scope mixin MixinTemplate!(...);


or maybe

scope mixin MixinTemplate(...){...}

mixin MixinTemplate!(...);