Given the following declarations:


  type M is (A, E);

  type R (D: M := M'First )is  record
    case D is
      when A => AS: Integer;
      when E => ES: Float;
    end case;
  end record;

  subtype RA is r (A);
  subtype RE is R (E);

  procedure Ass (D: M; Z: out R) is
    case D is
      when A => Z := (A, 1);
      when E => Z := (E, 1.0);
    end case;
  end Ass;

  procedure AssA (Z: out RA) is
    Z := (A, 1);
  end AssA;

  procedure AssE (Z: out RE) is
    Z := (E, 1.0);
  end AssE;

  procedure AssAE (D: M; Z: out R) is
    case D is
      when A => AssA (Z);
      when E => AssE (Z);
    end case;
  end AssAE;

  Z: R;

  ZA: R (A);
  ZE: R (E);


  Ass (E, Z);     -- ok

  AssAE (A, Z);   -- Constraint_Error, discriminant E
  AssAE (A, ZA);  -- ok


What is the deeper reason for the rules RM_95 6.4.1(14,16)) forcing that
for out parameters with constrained formals, the discriminant of the actual
must match already before the call, for unconstrained formals the dicriminant
of the actual changes as appropriate?

I'm aware of AARM_95 6.4.1(17e).

                                 o     _      _          _
 --------- __o       __o      /\_    _ \\o   (_)\__/o   (_)
 ------- _`\<,_    _`\<,_    _>(_)  (_)/<_     \_| \    _|/' \/
 ------ (_)/ (_)  (_)/ (_)  (_)         (_)    (_)     (_)'  _\o_
Mein Radunfall
My bike accident

Christoph Grein
Mitglied von Ada-Deutschland
Member of Ada Germany
eMail: [log in to unmask]