How to implement multiple inheritance in delphi?

Question

I\'m doing a full rewrite of an old library, and I\'m not sure how to handle this situation (for the sake of being understood, all hail the bike analogy):

I have the

Answer 1

Another alternative with newer versions of Delphi is to leverage generics in a compositional model. This is particularly useful in the case where the multiple base classes (TBarA and TBarB in this example) are not accessible for modification (ie: framework or library classes). For example (note, the necessary destructor in TFoo is omitted here for brevity) :

program Project1;

uses SysUtils;

{$APPTYPE CONSOLE}

type    
  TFooAncestor  = class
    procedure HiThere; virtual; abstract;
  end;
  TBarA = class(TFooAncestor)
    procedure HiThere; override;
  end;
  TBarB = class(TFooAncestor)
    procedure HiThere; override;
  end;
  TFoo = class
    private
      FFooAncestor: T;
    public
      constructor Create;
      property SomeBar : T read FFooAncestor write FFooAncestor;
  end;

procedure TBarA.HiThere;
begin
  WriteLn('Hi from A');
end;

procedure TBarB.HiThere;
begin
  WriteLn('Hi from B');
end;

constructor TFoo.Create;
begin
  inherited;
  FFooAncestor := T.Create;
end;

var
  FooA : TFoo;
  FooB : TFoo;
begin
  FooA := TFoo.Create;
  FooB := TFoo.Create;
  FooA.SomeBar.HiThere;
  FooB.SomeBar.HiThere;
  ReadLn;
end.