[SOLVED] Using nested type declared in a generic class within the generic interface that the class is implementing

Using nested type declared in a generic class within the generic interface that the class is implementing

I have a generic List-like class tMyList<B> with a method Each() which iterated over each element and calls anonymous procedure tMyList<A>.enumProc with paramenter - the current item of type <B>. I want to implement the class as an Interface for easier lifetime management.

The problem is I cannot declare the Each method in the iMyList<A> interface, because tMyList<A>.enumProc type is unknown. As far as I know Interfaces does not support nested types?

Here is the code:

  tMyList<B> = class;

  iMyList<A> = interface
    procedure each(enumProcedure: iMyList<A>.enumProc); // ERROR - Undeclared identifier: 'enumProc'
  end;

  tMyList<B> = class(tInterfacedObject, iMyList<B>)
    type
      enumProc = reference to procedure(item: iMyList<B>);
    public
      procedure each(enumProcedure: enumProc);
  end;

* Implementing Enumerator is not an option in this particular case

Solution

The only way that you can make this work is to define the procedural type outside of the implementing class. Like this:

type
  IMyIntf<A> = interface;

  TMyProc<A> = reference to procedure(Intf: IMyIntf<A>);

  IMyIntf<A> = interface
    procedure Foo(Proc: TMyProc<A>);
  end;

  TMyClass<A> = class(TInterfacedObject, IMyIntf<A>)
    procedure Foo(Proc: TMyProc<A>);
  end;