change mixins

[Denis Koroskin]

On Mon, 15 Feb 2010 00:31:29 +0300, Walter Bright  
<newshound1 at digitalmars.com> wrote:

> Right now, mixins are defined and used as:
>
>     template foo(T) { declarations... }
>
>     mixin foo!(int) handle;
>
> The proposal is to switch it around:
>
>     mixin template foo(T) { declarations... }
>
>     foo!(int) handle;
>
> to follow the notion that mixin templates are very different from  
> regular templates, and that should be reflected in their definition  
> rather than use.
>
> What do you think?

I support the change, expect that I believe mixing in the mixin template  
should involve the "mixin" keyword.

In fact, I have proposed exactly the same more that a year ago. Here is a  
quote:

Usually templates and mixin templates are completely
different, mixin'ing usual template or instantiating template that is
intended for being mixed-in makes no sense in the majority of real cases.
Moreover, I would prefer to separate these terms and so their syntax:

mixin template Bar
{
      private int value;
      public int getValue() { return value; }
}

class Foo
{
      mixin Bar!();
}

int bar = Bar!().getValue(); // Error: can't instantiate mixin template

template Square(alias x)
{
      private enum temp = x * x;
      public enum Square = temp;
}

class Test
{
      mixin Square!(42); // Error: can't mixin non-mixin template
}