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

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!(...);