Subtypes and type invariants in Ada2012

[Victor Porton <porton@narod.ru>]

I thought that type invariants are designed for subtypes. I mistook!

--
package X is

  type T is tagged private;

  function F(P: T) return Integer;

  subtype S is T with Type_Invariant => F(T) > 10;

private

  type T is tagged
    record
      X: Integer;
    end record;

end;
--

This does not verify:

$ gnatgcc -c -gnat2012 x.ads
x.ads:7:23: aspect "Type_Invariant" only allowed for private type or 
corresponding full view

So, my question: Is it possible to restrict a subtype with something like a 
type invariant?

I want a subtype restricted by an arbitrary condition. Is it possible?

-- 
Victor Porton - http://portonvictor.org