Re: Ada Successor Language

["J-P. Rosen" <rosen@adalog.fr>]

Le 24/06/2018 à 09:34, Dmitry A. Kazakov a écrit :
> That is not possible because generic formal contracts are weakly typed.
> Consider, for simplicity, this:
> 
>    with Ada.Finalization;
>    generic
>       type T is new Ada.Finalization.Controlled with private;
>    package P is
>       type S is new T with null record;
>       not overriding procedure Foo (X : S);
>    end P;
> 
> If the given descendant of Controlled has Foo already, you are out of
> luck. The contract says: any descendant of Ada.Finalization.Controlled.
> That is a lie.
You really need to understand the rules: "assume the best" in generic
specifications, "assume the worse" in generic bodies.

i.e. a generic spec is legal if there is at least one legal
instantiation. This is because the user is assumed to see the
specification, and therefore understand why some instantiation is rejected.

a generic body is illegal if there is at least one illegal
instantiation. This is because the user is not assumed to see the body
of a generic.

Hint: a generic can be made legal by moving some declarations from the
body to the specification (even into the private part).

-- 
J-P. Rosen
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