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From: "John B. Matthews" <nospam@nospam.invalid>
Newsgroups: comp.lang.ada
Subject: Re: prefix of dereference must be a name?
Date: Thu, 30 Jul 2009 15:35:02 -0400
Organization: The Wasteland
Message-ID: <nospam-96AE3E.15350230072009@news.aioe.org>
References: <u4osuzlxw.fsf@stephe-leake.org>
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Date: 2009-07-30T15:35:02-04:00
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In article <u4osuzlxw.fsf@stephe-leake.org>,
 Stephen Leake <stephen_leake@stephe-leake.org> wrote:

> I'd like to be able to do the following:
> 
> type T is record ... end record;
> type T_Access is access all T;
> 
> function "+" (Left, Right in : ...) return T_Access;
> 
> A : T_Access := new T;
> B : T_Access := new T;
> C : T_Access := A + B;
> 
> A.all := (C + B).all;
> 
> but GNAT complains that "prefix for selection is not a name", pointing
> to (C + B).all.
> 
> So then I tried:
> 
> function "-" (Token : in T_Access) return T_Access
> is begin
>     return Token;
> end;
> 
> A.all := -(C + B).all;
> 
> and got the same error. Finally I tried:
> 
> function Copy (Token : in T_Access) return T_Access
> is begin
>     return Token;
> end;
> 
> A.all := Copy (C + B).all;
> 
> And the compiler was happy.

Interesting. The compiler was happy with a function call:

A.all := "+"(C, B).all;

but a use_type_clause didn't seem to help.

> What's the rationale for this? 
> 
> I assume one issue here is that "-" might be an intrinsic, but since
> the type involved is not a numeric type, I don't see how that could be
> a problem.
> 
> Similarly for ().all; when could that be a problem?

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>