On 18/02/2021 22:42, Sven Barth wrote:
You need to constrain T as a TObject, then it works.
Ah that works. With 2 restrictions
TBase can be any class, since a trait can be applied to any class.
So the only known common base is TObject.
(restriction 1)
But "TBase: TObject" means that the trait can not access Self.Base, even
if the latter passed in type has such a method.
Same with (note the "class" keyword)
generic TTrait<TBase: class; THost> = class(TBase)
Normally if the param to a generic is not restricted you can write
T.anything, and during specialization this will be resolved or fail.
So that ability is lost.
As a workaround THost can be passed in.
(restriction 2)
That requires a forward declaration of TFoo. Otherwise it fails.
type
TFooBase = class
procedure Base;
end;
generic TTrait<TBase: TObject; THost> = class(TBase)
procedure Bar;
end;
TMyFoo = class;
TMyFoo = class(specialize TTrait<TFooBase, TMyFoo>)
procedure Foo;
end;
procedure TTrait.Bar;
begin
//Self.Base; // fails
THost(Self).Base;
THost(Self).Foo;
end;
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