On 25/07/2025 15:20, Mattias Gaertner via fpc-devel wrote:
On 7/25/25 13:44, Martin Frb via fpc-devel wrote:
Currently you can't do
type
generic TFoo<A> = class
procedure Bar; virtual;
end;
generic FooChild<F: TFoo> = class(F)
procedure Bar; override;
end;
Can you use:
generic FooChild<T> = class(specialize TFoo<T>)
procedure Bar; override;
end;
?
No.
One example is that I have several
TItem1, TItem2, TItem3,...
and for each a
TItem1List = specialize TFpgList<TItem1>;
But I don't actually use TItem1, ....
I use
TMyFinalItem1 =
specialize TFeatureX<
specialize TFeatureY<
specialize TFeatureZ< TItem1 >
>
>;
And each list needs to be
TMyFinalItem1 =
specialize TFeatureXForList<
specialize TFeatureYForList<
specialize TFeatureZForList< specialize TFpgList<TItem1> >
>
>;
Currently I can swap the order, and git it working by creating a non
generic base.... But that introduces dependencies that were not wanted...
Also, the error by the compiler is
Error: Generics without specialization cannot be used as a type
for a variable
But
generic FooChild<F: TFoo> = class(F)
- F is not a variable
- TFoo in not a type (for somethnig), TFoo is a constraint
If that syntax was allowed, it should mean that
- F must be of any type that is (a descendand of) a specialization of TFoo.
So this is NOT to allow FooChild to be specialized with another generic,
but with a (any) specialization of that generic.
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