Ethan Yager

I can't seem to implement the visitor pattern in Delphi without circular references. Does anyone know of a way to implement the visitor pattern without having all of the classes in one big unit? For instance, if I have a complex tree structure (psuedo code so that I can demonstrate concisely): Unit Base type TBase = class end; ------------------------------------------------------- Unit Bolt uses Base; TBolt = class(TBase) procedure Tighten; procedure Untighten; Visit(visitor: TAutomobileVisitor); <-- Requires circular reference to Automobile unit end; ------------------------------------------------------- Unit Door uses Base, Bolt; type TDoor = class(TBase) Bolts: array of TBolt; procedure Open; procedure Close; Visit(visitor: TAutomobileVisitor); <-- Requires circular reference to Automobile unit end; ------------------------------------------------------- Unit Seat uses Base, Bolt; type TSeat = class(TBase) Bolts: array of TBolt; procedure Heat(on: boolean); Visit(visitor: TAutomobileVisitor); <-- Requires circular reference to Automobile unit end; ------------------------------------------------------- Unit Automobile uses Base, Door, Seat, Bolt; type TAutomobile = class(TBase) FOwnerName: string; Doors: array of TDoor; Seats: array of TSeat; Visit(visitor: TAutomobileVisitor); end; TAutomobileVisitor = class procedure Visit(o: TAutomobile); overload; virtual; procedure Visit(o: TBolt); overload; virtual; procedure Visit(o: TDoor); overload; virtual; procedure Visit(o: TSeat); overload; virtual; end; ------------------------------------------------------- I have tried moving things around and using interfaces but can't seem to avoid circular references.