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From: adam@irvine.com (Adam Beneschan)
Newsgroups: comp.lang.ada
Subject: Re: Renaming an abstract function
Date: 16 Nov 2001 19:08:04 -0800
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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.  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.  "callable entity" is easily found in the index.
 
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.

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