Function traits at compile time

[Oskar Linde]

Victor Nakoryakov skrev:
> Hi all,
> 
> Consider code:
> 
> class MyClass(StructT)
> {
> ...
> }
> 
> I know, that StructT has a function `foo` in it, but I don't know number 
> of parameters and their types, of course. Does anybody knows a way to 
> extract types to use them in `static if ( is(...) )` statements?

Hi,

This is possible but a bit tricky. You can use the compiler IFTI support 
to extract this information. Make a template such as:

template delegateInfo(Ret, T1, T2, T3) {
     Something!(Ret,T1,T2,T3) delegateInfo(Ret delegate(T1,T2,T3) x) {}
}

The template Something can then contain aliases for the different 
argument types.

http://www.digitalmars.com/drn-bin/wwwnews?digitalmars.D/38553 has 
already implemented such templates for you (just change the function 
argument -> delegate and you should be able to do things like:

class MyClass(StructT) {
	static if (funcInfo(&StructT.init.foo).numArgs == 1) {
		pragma(msg,"StructT.foo takes 1 argument");
         }
         static if (is(typeof(funcInfo(&StructT.init.foo).Arg0Type)
                       == int)) {
                 pragma(msg,"First argument to StructT.foo is an int");
         }
}

/Oskar