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!feeder.eternal-september.org!border1.nntp.ams1.giganews.com!nntp.giganews.com!news.unit0.net!news.mixmin.net!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Instantiations of a generic with often encountered arguments
Date: Sun, 26 Nov 2017 09:52:35 +0100
Organization: Aioe.org NNTP Server
Message-ID: <ovdvck$2r4$1@gioia.aioe.org>
References: <ovd0dt$hmi$1@gioia.aioe.org>
NNTP-Posting-Host: MajGvm9MbNtGBKE7r8NgYA.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
X-Notice: Filtered by postfilter v. 0.8.2
Content-Language: en-US
Xref: feeder.eternal-september.org comp.lang.ada:49147
Date: 2017-11-26T09:52:35+01:00
List-Id: <comp.lang.ada>

On 2017-11-26 01:04, Victor Porton wrote:
> Is it a good practice to declare "centralized" (that is in the same package
> as a generic packages is defined in, or in a child unit) instantiations of a
> generic package with common (that is often encountered, such as Integer,
> String, etc.) generic parameters?

Yes, Ada library does so for standard types.

Sometimes a set of related generic packages is instantiated in a third 
package which is then used. E.g. you have a generic vector, matrix, 
solver defined over the same type.

> In C++ this is not a problem, because there a template is instantiated
> whenever one needs it.

Because in C++ templates are 100% macros, whereas in Ada generic 
instances can be shared, theoretically at least, and should be treated 
as real packages.

Then C++ templates have structrual matching, all instances/expansions 
with same parameters are same. It is no matter where you would expand a 
macro. Ada uses nominal matching of generic instances and they can be 
scoped.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de