Klassen sollen sich gegenseitig kennen

[Der schöne Günther]

Delphi-Quellcode:

uses
  Generics.Collections;

type
   MyParent = Class;   // This is a forward class definition

  MyChild = Class
  private
    ParentObect:MyParent;
  public
  End;

  MyParent = Class // The MyParent class is now defined
  public
    tlChildren:TList<MyChild>;
  end;

implementation

end.

Quelle:
http://stackoverflow.com/a/2137057