From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!gandalf.srv.welterde.de!news.jacob-sparre.dk!loke.jacob-sparre.dk!pnx.dk!.POSTED!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: What is the purpose of Vector.Query_Element?
Date: Mon, 27 Jul 2015 15:12:18 -0500
Organization: Jacob Sparre Andersen Research & Innovation
Message-ID: <mp63b3$9t8$1@loke.gir.dk>
References: <ca22434f-8216-4cbd-a4c0-46fea8e6cc98@googlegroups.com>
NNTP-Posting-Host: rrsoftware.com
X-Trace: loke.gir.dk 1438027939 10152 24.196.82.226 (27 Jul 2015 20:12:19 GMT)
X-Complaints-To: news@jacob-sparre.dk
NNTP-Posting-Date: Mon, 27 Jul 2015 20:12:19 +0000 (UTC)
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157
Xref: news.eternal-september.org comp.lang.ada:27047
Date: 2015-07-27T15:12:18-05:00
List-Id: <comp.lang.ada>

"EGarrulo" <egarrulo@gmail.com> wrote in message 
news:ca22434f-8216-4cbd-a4c0-46fea8e6cc98@googlegroups.com...
> The package that defines Vector provides this procedure:
>
> procedure Query_Element
>  (Container : in Vector;
>   Index : in Index_Type;
>   Process : not null access procedure (Element : in Element_Type));
>
> Why is this procedure provided?  Isn't `Query_Element (Vector, Index, 
> Process'Access)` the same as `Process (Element (Vector, Index))`?

Sure, if you don't care about performance they're the same. But a function 
result is a copy of the element ("Element" is a function), whereas 
Query_Element can pass the element by reference (and will for most types 
that aren't by-copy); in that case it is directly referenced in place. For 
large elements (say, like other containers), the overhead of copying could 
be considerable. OTOH, if the element is a by-copy type, there is no 
difference. So Query_Element is a specialized need. Besides, for Ada 2012, 
you probably ought to be using the indexing syntax and not use either of 
these.

                                Randy.