On 18/02/2021 18:46, Ryan Joseph via fpc-pascal wrote:
On Feb 18, 2021, at 10:40 AM, Benito van der Zander via fpc-pascal
<fpc-pascal@lists.freepascal.org> wrote:
Traits are like reverse type helpers. With the type helper you first declare
the class and then the extending helper.
Indeed, but with the crucial distinction that helpers don't allow fields, only
methods.
And they are differently scoped.
There is another approach, but generics do not yet support that
type
TFooBase = class
end;
TTrait = trait
procedure Bar;
end;
TFoo = class(TFooBase)
_trait: TTrait;
procedure Foo;
end;
could be written as
generic TTrait<T> = class(T)
procedure Bar;
end;
TMyFoo = class(specialize TTrait<TFooBase>)
procedure Foo;
end;
Of course that can get out of hand, if you want to include many traits.
---------
On the other hand, it even would allow support for the Trait to access
methods from TFoo...
generic TTrait<TBase, THost> = class(TBase)
procedure Bar; // can do THost(self).Foo()
end;
TMyFoo = class(specialize TTrait<TFooBase, TMyFoo>)
procedure Foo; // can call Bar()
end;
Of course assuming that TMyFoo can already be passed during specialization.
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