Ok my summary thus far with this syntax (default interface delegation) is that
composition is possible (which is very nice) but polymorphism is not really
possible so it's not exactly an alternative to multiple inheritance. Besides
the complications of implementing method resolution for classes (no idea what's
involved here) I would say it's a pretty low time investment to get a good
chunk of what people want from multiple inheritance, although not a full
fledged alternative like adding a new "trait" syntax would provide.
I want to add more examples to the GitHub page so we don't forget. The most
important thing to get right is not allowing any possibility to write have
ambiguous methods. Here are some common ones I could think of. Are these
correct? Anything to add? I guess the compiler just gives "already declared"
errors for each method with a conflict. Does the visibility of the property
matter in subclasses (I assume yes)?
(****************************************************************************************)
type
ICircle = interface
procedure Draw;
end;
type
TCircle = record
procedure Draw;
end;
type
TMyShape = class(ICircle)
private
FCircle: TCircle;
public
property Circle: TCircle read FCircle implements ICircle; default;
end;
type
TOtherShape = class(TMyShape)
public
// ERROR - draw is already declared
procedure Draw;
end;
(****************************************************************************************)
type
TMyShape = class(ICircle)
private
FCircle: TCircle;
public
property Circle: TCircle read FCircle implements ICircle; default;
// ERROR - Draw already declared
procedure Draw;
end;
(****************************************************************************************)
type
TMyShape = class(ICircle)
private
FCircle: TCircle;
public
property Circle: TCircle read FCircle implements ICircle; default;
// Conflict is resolved, we can now redeclare Draw and Circle.Draw will
point to TMyShape.Draw instead of TCircle.Draw
procedure ICircle.Draw = Draw;
procedure Draw;
end;
(****************************************************************************************)
type
ISquare = interface
procedure Draw;
end;
type
TSquare = record
procedure Draw;
end;
type
TOtherShape = class(TMyShape, ISquare)
private
FSquare: TSquare;
public
// ERROR - Draw is already declared
property Square: TSquare read FSquare implements ISquare; default;
end;
Regards,
Ryan Joseph
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