> On Feb 18, 2021, at 3:07 PM, Sven Barth <pascaldra...@googlemail.com> wrote:
>
>> So "class type method resolution" is what's missing? I never used the
>> interface method resolution so I don't really understand this feature. What
>> needs to happen as far as the compiler is concerned?
>
> The problem is this: if you have a property with an interface type the
> compiler can simply build the interface's VMT for this. However for classes
> (or objects or records) the compiler needs to generate slightly different
> thunks that fixup the correct Self value, especially if things are mixed
> between the subclass and the container class.
Then this is the real challenge to implement a "default implements property"
and something I know nothing about. :) The rest is pretty easy actually though.
>
>> type
>> TMyShape = class(TShape, ICircle)
>> private
>> m_circle: TCircle;
>> protected
>> procedure ICircle.Draw = Draw;
>> public
>> property circle: TCircle read m_circle implements ICircle;
>> end;
>
> Your specific example is rather useless, cause your interface only has a
> single method that you redirect to the class' method thus you wouldn't need
> to use interface delegation. But anyway, your code would generate a runtime
> error, because your TMyShape.Draw would still be abstract.
Maybe it's a bad example but I'm trying to illustrate how method resolution
could be used for overriding (or what ever it would be called in this context.
I know this isn't correct syntax but it's more of this direction:
procedure Draw = ICircle.Draw;
TShape.Draw is resolved by ICircle.Draw, which is implemented via TCircle. It's
quasi-overriding but the VMT table should point to m_circle.Draw so Draw could
be called on TShape and get property resolved by the "implements ICircle"
property. Hope that makes sense.
Regards,
Ryan Joseph
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