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From: =?ISO-8859-1?Q?Yannick_Duch=EAne_Hibou57?= <yannick_duchene@yahoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: prefix of dereference must be a name?
Date: Thu, 30 Jul 2009 10:36:41 -0700 (PDT)
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Date: 2009-07-30T10:36:41-07:00
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On 30 juil, 09:09, Stephen Leake <stephen_le...@stephe-leake.org>
wrote:
> [...]
> A.all :=3D (C + B).all;
>
> [...]
> So then I tried:
> [...]
> A.all :=3D -(C + B).all;
>
> and got the same error. Finally I tried:
>
> [...]
> A.all :=3D Copy (C + B).all;
>
> And the compiler was happy.
>
> What's the rationale for this?
>
> [...]
> Similarly for ().all; when could that be a problem?
>
> --
> -- Stephe

Hi Stephe,

The reason behind this is in the language reference.

Let's go step by step.

First of all ARM 4.1.3 says:
(2) selected_component ::=3D prefix . selector_name
(3) selector_name ::=3D identifier | character_literal | operator_symbol

No special point with =93 selector_name =94 and any way, you did not get
into trouble with it.

Next, is the =93 prefix =94 part which is of big interest to you.

About it, ARM 4.1 says:
(2) name ::=3D
     direct_name | explicit_dereference
   | indexed_component | slice
   | selected_component | attribute_reference
   | type_conversion | function_call
   | character_literal


You may open you ARM reference or you may browse it at
http://www.adaic.com/standards/05rm/html/RM-TTL.html is you haven't
got one off-line on computer and then go to ARM 4.1 and follow each
links to know in detail about what the =93 name =94 part can be.

But you can see in the latter excerpt, that =93 function_call =94 appears,
but not =93 expression =94.

Now about the rationale behind (previously given, was the direct
reason), I do not know, but I guess this may be to avoid any kind of
invisible temporaly variable (the result of a function is mostly an
initializer, not a returned variable).

If I find more about the rational, I will tell you, or perhaps some
one else will tell before ;)

Have a nice time

Yannick