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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: RegEx / rename of a function result
Date: Wed, 6 Jul 2022 19:44:11 -0500
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"Thomas" <fantome.forums.tDeContes@free.fr.invalid> wrote in message 
news:62c5b5e9$0$22251$426a34cc@news.free.fr...
> In article <a6e2e912-8aa6-4ecf-9118-9dd29a967734n@googlegroups.com>,
> Shark8 <onewingedshark@gmail.com> wrote:
>> > The RENAME is interesting as I have not seen that before. Is it a 
>> > rename of
>> > the function call (invokes the function upon reference) or a rename of 
>> > the
>> > function result?
>> That form of RENAMES is the function result.
>> I've found it an excellent alternative to CONSTANT, as it signals my 
>> intent
>> to have an alias for some result inside DECLARE blocks and certain 
>> internal
>> objects. (eg Default_Map : Map renames Internal_Map_Generation(P1, P2); 
>> ...
>> and then I can use "Default_Map" instead of calling the 
>> generation-function
>> at each point and possibly messing things up should the parameters 
>> change.)
>
> why renames is better than constant in this case ?
> could you explicit the difference between them, please?

In theory, a renames captures the function result object, so for a composite 
type, you avoid copying it. That can be especially significant for 
controlled types, where you avoid an extra Finalization (and that might be 
critical if you are implementing Finalize). I believe there also are some 
accessibility differences that might matter in unusual cases.

In most cases, however, they are essentially the same, generating 
essentially the same code. So it is a matter of preference which to pick. (I 
usually use "constant" unless avoiding a copy is necessary.)

                                 Randy.