While playing around with templates and alias parameters, I got the die of trying this:

struct foo(alias T)
{
  typeof(T) opAddAssign(typeof(T) rhs)
  {
    return T += rhs;
  }
}

class bar
{
private:
  int _baz;
public:
  foo!(_baz) baz;
}

When compiling this, I get the message "Error: this for_baz needs to be type bar not type foo!(_baz)*"

Is there a workaround to this, or even a plan to make such things possible in the future?

-- Simen

"Simen Kjaeraas" <simen.kjaras@gmail.com> wrote in message news:fvfg2g$1nnp$1@digitalmars.com...
> While playing around with templates and alias parameters, I got the die of trying this:
>
> struct foo(alias T)
> {
>  typeof(T) opAddAssign(typeof(T) rhs)
>  {
>    return T += rhs;
>  }
> }

If you make this a template:

template foo(alias T)
// rest is the same

>
> class bar
> {
> private:
>  int _baz;
> public:
>  foo!(_baz) baz;

And now change this to a mixin:

mixin foo!(_baz) baz;

It works.

Of course, this has the effect of making foo (or rather an instance of foo) no longer a type.  But maybe you don't need it to be.

Jarrett Billingsley Wrote:

> "Simen Kjaeraas" <simen.kjaras@gmail.com> wrote in message news:fvfg2g$1nnp$1@digitalmars.com...
> > While playing around with templates and alias parameters, I got the die of trying this:
> >
> > struct foo(alias T)
> > {
> >  typeof(T) opAddAssign(typeof(T) rhs)
> >  {
> >    return T += rhs;
> >  }
> > }
> 
> If you make this a template:
> 
> template foo(alias T)
> // rest is the same
> 
> >
> > class bar
> > {
> > private:
> >  int _baz;
> > public:
> >  foo!(_baz) baz;
> 
> And now change this to a mixin:
> 
> mixin foo!(_baz) baz;
> 
> It works.
> 
> Of course, this has the effect of making foo (or rather an instance of foo) no longer a type.  But maybe you don't need it to be.

Now why didn't I think of that... I have to say the mixin syntax is uglier, but it gets the job done.

There are times when I wish I could declare a function, template or whatever to be a mixin type, so any instantiation of it would be a mixin. If that were to be implemented, I wouldn't have the ugly 'mixin' keyword cluttering my code. It would make code cleaner, but mayhaps more hard to read.

-- Simen