Given the following declarations:

declare

  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
  begin
    case D is
      when A => Z := (A, 1);
      when E => Z := (E, 1.0);
    end case;
  end Ass;

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

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

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

  Z: R;

  ZA: R (A);
  ZE: R (E);

begin

  Ass (E, Z);     -- ok

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

end;

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
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