Version 1.1 of ai05s/ai05-0222-1.txt

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!standard 3.9.2(13) 10-10-20 AI05-0222-1/01
!standard 13.14(16)
!class binding interpretation 10-10-20
!status work item 10-10-20
!status received 10-03-25
!priority Low
!difficulty Easy
!qualifier Error
!subject A completion of a primitive subprogram can occur after freezing

!summary

A completion of a primitive subprogram of a tagged type can occur after the freezing of the tagged type.

!question

Consider:

package Pak1 is type T1 is tagged record ... end record; procedure Op (X : in out T1); end Pak1;

with Pak1; procedure Proc2 is

type T2 is new Pak1.T1 with record ... end record; overriding procedure Op (X : in out T2);

Var : T2;

overriding procedure Op (X : in out T2) is -- (A) begin ... end Op;

...

3.9.2(13): "The explicit declaration of a primitive subprogram of a tagged type shall occur before the type is frozen."

6.3(5): "A subprogram_body is considered a declaration. It can either complete a previous declaration, or itself be the initial declaration of the subprogram."

one could think that since line (A) is a declaration, it's overriding a primitive subprogram, and it's occurring after the type is frozen, that 3.9.2(13) makes it illegal.

That clearly makes no sense; should this be fixed? (Yes.)

!wording

Modify 3.9.2(13):

The explicit declaration {that is not a completion} of a primitive subprogram of a tagged type shall occur before the type is frozen (see 13.14). For example, new dispatching operations cannot be added after objects or values of the type exist, nor after deriving a record extension from it, nor after a body.

Modify 13.14(16):

The explicit declaration {that is not a completion} of a primitive subprogram of a tagged type shall occur before the type is frozen (see 3.9.2).

!discussion

The example in the question is a pathology.

Subprograms in a package body are not primitive, but may complete a primitive subprogram, so it is arguable if these rules apply to them (clearly, they were not intended to).

But the introduction of expression functions by AI05-0177-1 makes this a more significant problem. We would not want the following to be illegal:

package Pak2 is type T is tagged private; function F (Obj : T) return Boolean; private type T is tagged record Flag : Boolean; end record; Object : T; -- Freezes T. function F (Obj : T) return Boolean is (Obj.Flag); end Pak2;

So we need to fix this.

!ACATS Test

An ACATS test could be constructed for the expression function case (the example of the question is too much of a pathology to matter).

!appendix


!topic Subprogram body declarations and 3.9.2(13)
!reference RM 3.9.2(13), 13.14(16), 6.3(5)
!from Adam Beneschan 10-03-25
!discussion


This is a wording nitpick that I'm not sure really needs to be fixed: 

    package Pak1 is
       type T1 is tagged record ... end record;
       procedure Op (X : in out T1);
    end Pak1;

    with Pak1;
    procedure Proc2 is

       type T2 is new Pak1.T1 with record ... end record;
       overriding
       procedure Op (X : in out T2);

       Var : T2;

       overriding
       procedure Op (X : in out T2) is       -- (A)
       begin
          ...
       end Op;

    ...

Shouldn't cause any problems, right?  Op (on T2) is declared before
Var, which is before T2 is frozen.

However, the way things are worded:

3.9.2(13): "The explicit declaration of a primitive subprogram of a
tagged type shall occur before the type is frozen."

6.3(5): "A subprogram_body is considered a declaration.  It can either
complete a previous declaration, or itself be the initial declaration
of the subprogram."

one could think that since line (A) is a declaration, and it's
occurring after the type is frozen, that 3.9.2(13) makes it illegal. 

Perhaps the intent is so obvious that no fix is needed; but if it's
considered incorrect, then changing 3.9.2(13) and 13.14(16) to
something like

   The explicit declaration (that is not the completion of a previous
   declaration) of a primitive subprogram of a tagged type shall occur
   before the type is frozen.

would work.

****************************************************************

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