Re: Renaming an abstract function

[Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>]

adam@irvine.com (Adam Beneschan) writes:

> Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> wrote in message news:<uvggau5ro.fsf@gsfc.nasa.gov>...
> > "Nick Roberts" <nickroberts@adaos.worldonline.co.uk> writes:
> > 
> > > When given the program:
> > > 
> > >    package Test1 is
> > >       type T is abstract tagged limited private;
> > >       function P (X, Y: in T) return T is abstract;
> > >       function "*" (A, B: in T) return T renames P; -- error line
> > >    private
> > >       type T is abstract tagged limited null record;
> > >    end;
> > > 
> > > GNAT 3.12p on Windows 95 returns the error message:
> > > 
> > >    function that returns abstract type must be abstract
> > > 
> > > Is this a bug in: (a) GNAT; (b) the RM95; or (c) my brain?
> > 
> > Same error in gnat 3.14 (you should at least upgrade to 3.13p).
> > 
> > RM 8.5.4 (2) says:
> > 
> >   2.      subprogram_renaming_declaration ::=
> >              subprogram_specification renames callable_entity_name;
> > 
> > The term "callable_entity_name" is not mentioned elsewhere in the
> > reference manual, which I find odd.
> 
> Note that "callable_entity" is in italics, while "name" is not.  

Well, not in the info version :). Guess there's a use for html, after
all :).

> In RM notation, that means that the language expects the syntax of a
> "name" (defined in 4.1), while "callable_entity" is a description
> that tells you what the name has to represent. I guess if you're
> searching a text file version of the RM, there's probably no
> indication that part of it is in italics. 

Yes; "info format" is ASCII with hyperlinks. Nice for reading from
Emacs. But it does lose the italics. Hmm, Emacs 21.1 can probably do a
better job of displaying the html version; I'll try that. 

> "callable entity" is easily found in the index.

Ah. I didn't think of that.

> A "callable entity" is defined (in 6(2)) to be a subprogram or
> entry. Thus an abstract subprogram is a callable entity even though
> you can't really call it.

Ok.

> I don't see any prohibition on renaming an abstract subprogram.
> However, renaming subprograms don't quite take on all the
> characteristics of the subprograms they rename; see 8.5.4(12) for
> instance. I suspect that has something to do with why renaming an
> abstract subprogram could lead to an error, but I don't have time
> right this minute to look into it further.
> 
> 				-- Adam

-- 
-- Stephe