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=-0.3 required=5.0 tests=BAYES_00,HK_RANDOM_FROM,
	INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,fcf8ea94b94d6941
X-Google-Attributes: gid103376,public
From: bglbv@my-dejanews.com
Subject: Re: Modular type. What is it and why?
Date: 1999/04/06
Message-ID: <871zhxmlaw.fsf@bglbv.my-dejanews.com>#1/1
X-Deja-AN: 463406715
References: <7ean3c$79m$1@eol.dd.chalmers.se> <7eb2iq$jc3@hobbes.crc.com>
 <7ede2p$pd1$1@its.hooked.net> <370A4B3A.5EDB3B37@pwfl.com>
 <7edk6p$1j7$1@its.hooked.net>
X-Complaints-To: abuse@theplanet.net
X-Trace: news4.svr.pol.co.uk 923441984 5697 62.136.95.129 (6 Apr 1999 23:39:44
 GMT)
Organization: Customer of Planet Online
NNTP-Posting-Date: 6 Apr 1999 23:39:44 GMT
Newsgroups: comp.lang.ada
Date: 1999-04-06T23:39:44+00:00
List-Id: <comp.lang.ada>

"Mike Silva" <mjsilva@jps.net> writes:

> As Ole-Hjalmar Kristensen commented, the nice Ada solution doesn't work if
> NUM_ELEMENTS varies at runtime (at least, it appears that a modular type
> can't be defined dynamically -- correct?), but that's not the usual case I
> run across.

Correct: the standard requires the modulus to be a *static* expression.
There is a similar restriction for signed integer types (and fixed and
floating point types): presumably it would be too much trouble to have
to choose between, say, a 16-bit and a 64-bit representation at run time.
Subtypes, on the other hand, can have their constraints elaborated at
run time, but that doesn't let one change the modulus...