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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: When to use formal discrete type?
Date: Wed, 29 Nov 2017 15:05:59 -0600
Organization: JSA Research & Innovation
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Date: 2017-11-29T15:05:59-06:00
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"Victor Porton" <porton@narod.ru> wrote in message 
news:ovn0bv$1rto$1@gioia.aioe.org...
...
> It there a noticeable difference in performance if I generalize?

That clearly is compiler specific, and also specific to how the type is 
used.

Janus/Ada, for example, uses generic sharing, so the code generated for a 
formal discrete type and a formal private type are very different. (In most 
cases, the formal private type will win, but not if there are a lot of 
components of that type).

OTOH, GNAT generally uses template expansion. In such a case, the final code 
isn't much different than if you had written it yourself without using the 
generic. So it probably doesn't matter much.

The main difference is the promise given to the instantator. A private type 
implies that any non-limited type will work (assuming that it has the 
operations given in the generic spec). So you may want to consider what 
happens if someone instantiates your generic with some record type. If that 
would be a real problem, then the formal discrete type would be better (as 
it better documents what actually works).

                                   Randy.