Template interface containing template struct

Question

Given a struct template, and a template interface that has a member that returns the struct template as well as another member of a different type, what is the correct way to design and implement?

I've the following, but I'm getting compile errors on implementation:

struct TemplateStruct(T, U) {
  T a;
  U b;
}

interface IFoo(V) {
  TemplateStruct resulta();
  V resultb();
}

class Foo : IFoo!int {
  TemplateStruct!(bool, string) resulta() {
    return TemplateStruct!(bool, string)(true, "a");
  }

  int resultb() {
    return 1;
  }
}

Looking through the online Programming in D book doesn't cover implementing this sort of situation.

Answer 1

Here is your mistake:

interface IFoo(V) {
    TemplateStruct resulta(); // <== Here
    V resultb();
}

resulta() returns TemplateStruct, which is a template, not a full type. You'll need to specify its template parameters, like you do in class Foo:

interface IFoo(V) {
    TemplateStruct!(bool, string) resulta();
    V resultb();
}