[fpc-devel] [Feature Request] get nested type from a generic class

[Sven Barth]

Am 21.09.2012 03:57, schrieb ZAN DoYe:
> I wanna make a generic class that can generates all six relational
> operators with the passed in  class T which has only one lessThan
> operator. But fpc can't recognize blow code:
>
>      generic tLess<T>= class
>          public type
>              tT= T;
>          public
>              class function lessThan(const a, b: T): boolean;
>      end;
>
>      generic tCompOps<C>= class
>          public type
>              T= C.tT;                        //// Error: Error in type
> definition ////
>          public
>              class function equal(const a, b: T): boolean;
>              class function notEqual(const a, b: T): boolean;
>              class function lessThan(const a, b: T): boolean;
>              class function lessThanOrEqual(const a, b: T): boolean;
>              class function greaterThan(const a, b: T): boolean;
>              class function greaterThanOrEqual(const a, b: T): boolean;
>      end;
>
> I hope this feature could be implemented if it's possible.

If you already expect that "C" is a "tLess<Something>" then you should 
write it the following way:

=== source begin ===

// tLess<T> as in your example

generic tCompOps<T> = class
   public type
     TLessT = specialize tLess<T>;
   public
     // the remaining methods are like in your example with the 
exception that in the implementation you don't use type "C", but "TLessT"
end;

=== source end ===

Regards,
Sven