• Simen Kjaeraas <simen.kjaras gmail.com> May 02 2008
• "Jarrett Billingsley" <kb3ctd2 yahoo.com> May 02 2008
• Simen Kjaeraas <simen.kjaras gmail.com> May 02 2008

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