Shows a couple of different ways to check at compile time that a composed class inherits specific interfaces.

GenericComposition.d

void main() {}

class Provider {
	Concrete c;
}

class Concrete : HasThis, HasThat { }

interface HasThis {}
interface HasThat {}

void m(T)(T t) if(is(typeof(T.c) : HasThis)) {
}

class Provider2 : C{
	Concrete c;

	override Concrete getC() { return c; }
}

interface C {
	HasThat getC();
}

void m2(T : C)(T t) {
}

void foo() {
	m(Provider.init);
	m2(Provider2.init);
}

// This is a Compiler Error
class Provider3 : C {
	Concrete2 c;

	override Concrete2 getC() { return c; }
}

class Concrete2 : HasThis { }