Syntax of extended return statement

Syntax of extended return statement

[Bill Findlay]

I have the following compilation warning from GNAT:

   function pop
   return KDF9.word is
   begin
      the_nest_depth := the_nest_depth - 1;
      return result : KDF9.word := the_nest(the_nest_depth) do
             |
>>> warning: "result" is not modified, could be declared constant
         the_nest(the_nest_depth) := 0;
      end return;
   end pop;

If I change the return statement to:

      return result : constant KDF9.word := the_nest(the_nest_depth) do
         the_nest(the_nest_depth) := 0;
      end return;

it compiles without warning.

My problem is that I see no justification for that in the Ada 2005 RM, which
gives:

extended_return_statement ::=

return defining_identifier:[aliased] return_subtype_indication[:=expression]
[do
   handled_sequence_of_statements
end return]; 

return_subtype_indication ::= subtype_indication | access_definition

Can anyone enlighten me?

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;

Re: Syntax of extended return statement

[Robert A Duff]

Bill Findlay <news@findlayw.plus.com> writes:

> My problem is that I see no justification for that in the Ada 2005 RM, which
> gives:
>
> extended_return_statement ::=
>
> return defining_identifier:[aliased] return_subtype_indication[:=expression]
> [do
>    handled_sequence_of_statements
> end return]; 
...
> Can anyone enlighten me?

"constant" is allowed by AI05-0015.  If you look at the latest version
of the RM, you will see that syntax allowed.

- Bob

Re: Syntax of extended return statement

[Julian Leyh]

On 16 Mrz., 01:01, Bill Findlay <n...@findlayw.plus.com> wrote:
> I have the following compilation warning from GNAT:
>
>    function pop
>    return KDF9.word is
>    begin
>       the_nest_depth := the_nest_depth - 1;
>       return result : KDF9.word := the_nest(the_nest_depth) do
>              |>>> warning: "result" is not modified, could be declared constant
>
>          the_nest(the_nest_depth) := 0;
>       end return;
>    end pop;

"result" is not modified, so the warning is correct.

Re: Syntax of extended return statement

[Bill Findlay]

On 16/03/2011 02:23, in article wccoc5bkdmd.fsf@shell01.TheWorld.com,
"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote:

> Bill Findlay <news@findlayw.plus.com> writes:
> 
>> My problem is that I see no justification for that in the Ada 2005 RM, which
>> gives:
>> 
>> extended_return_statement ::=
>> 
>> return defining_identifier:[aliased] return_subtype_indication[:=expression]
>> [do
>>    handled_sequence_of_statements
>> end return]; 
> ...
> 
>> Can anyone enlighten me?
> 
> "constant" is allowed by AI05-0015.  If you look at the latest version
> of the RM, you will see that syntax allowed.

Aha! Out-of-date RM! Now I can sleep easy. 8-)

Thanks, Bob.

-- 
Bill Findlay
with blueyonder.co.uk;
use  surname & forename;