Hello,

I was wondering why the following does not work:

interface A(Type)
	{ Type blah(); }

template ADefaults(Type, AType : A!(Type))
{
	Type blah()
		{ return Type.init; }
}

class B(Type) : A!(Type)
	{ mixin ADefaults!(Type, B!(Type)); }

void main()
	{ auto x = new B!(int)(); }

It gives the error: test.d(11): mixin ADefault!(int,B) does not match any template declaration

However, it will compile if you change the ADefaults header to:

template ADefaults(Type, AType)

If the compiler can tell that B!(int) is a type, why can't it tell that it is a child class of A!(int) ?

Mike L. wrote:
> If the compiler can tell that B!(int) is a type, why can't it tell that it is a child class of A!(int) ?

This is a bug. In template specializations, : means equality. In static if, : means convertibility.

So, you can use:
template ADefaults(Type, AType)
{
	static assert (is (AType : A!(Type)));
	Type blah()
		{ return Type.init; }
}

http://d.puremagic.com/issues/show_bug.cgi?id=1715 if you want to vote.

Christopher Wright wrote:
> Mike L. wrote:
>> If the compiler can tell that B!(int) is a type, why can't it tell that it is a child class of A!(int) ?
> 
> This is a bug. In template specializations, : means equality. In static if, : means convertibility.

This is only with template specializations involving templates, by the way. Template specializations involving any other type are fine.