Are named variadic arguments possible?

[Lars T. Kyllingstad]

downs wrote:
> Alex wrote:
>> Is it possible, using templates, tuples, or some other mechanism, to implement named variadic arguments in D?
>>
>> For example, I'd like to be able to do something like...
>> foo( 2, &bar, age : 10, status : "down");
>>
>> and so forth.
> 
> Yes, with a small hack.
> 
> typedef int age_type;
> 
> age_type age(int i) { return cast(age_type) i; }
> 
> void foo(T...)(int i, Bar*, T t) {
>   // Test T for age_type here.
> }


In D2 this won't be possible for much longer, since typedef is going 
away. But you can fake it:

   template Typedef(T, string name)
   {
       mixin("struct "~name~" { "~T.stringof~" x; alias x this; }");
   }

   mixin Typedef!(int, "age_type");
   age_type age(int i) { return age_type(i); }

If you're going to use it a lot, you can even automate it further:

   template NamedArg(T, string name)
   {
       mixin Typedef!(T, name~"_type");
       mixin(name~"_type "~name~"("~T.stringof~" t) {"
	~" return "~name~"_type(t); }");
   }

   mixin NamedArg!(int, "age");
   mixin NamedArg!(string, "status");

   foo(2, &bar, age(10), status("down"));

-Lars