C++ Macro to D mixin template, delegates Please help

[Regan Heath]

BLS wrote:
> template ON_WM_CLOSE(D) (D delegate() dg)
> {
>     if (uID == WM_CLOSE)
>     {
>         lResult = dg();
>         return lResult;
>     }
> }

This seems to be mixing template syntax (using "template") with template 
function syntax (using "(D)(D delegate() dg)".  I don't think you want a 
template function so, rather something like:

template ON_WM_CLOSE(alias D)
{
     if (uID == WM_CLOSE)
     {
         lResult = D();
         return lResult;
     }
}

(see the duffs_device example here 
http://www.digitalmars.com/d/template-mixin.html)

However this wont work because a template body can only contain 
'declarations' which means;

Declaration:
         typedef Decl
         alias Decl
         Decl

Decl:
         StorageClasses Decl
         BasicType Declarators ;
         BasicType Declarator FunctionBody
	AutoDeclaration

So, you can put typedefs, aliases, variables and functions in a 
template, but, what you can't do is put an "if" statement in there.  So, 
templates and mixins in D just can't achieve the same effect as the 
C/C++ define macro can.

The planned/propsed D macro feature however, that should do what you 
want I reckon.

Regan