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=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,cea03ed275aa3d28,start
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news3.google.com!border1.nntp.dca.giganews.com!nntp.giganews.com!nx01.iad01.newshosting.com!newshosting.com!198.186.190.247.MISMATCH!news-out.readnews.com!news-xxxfer.readnews.com!not-for-mail
Newsgroups: comp.lang.ada
Subject: Question about generics.
From: "Peter C. Chapin" <pchapin@sover.net>
Organization: Kelsey Mountain Software
Message-ID: <Xns97F47B960CF95pchapinsovernet@198.186.192.137>
User-Agent: Xnews/5.04.25
Date: 02 Jul 2006 16:08:42 GMT
NNTP-Posting-Host: 2026f847.news.sover.net
X-Trace: 
 DXC=@<D>L1bV^5UaTW?f1gG?hTK6_LM2JZB_ShA^mA3hQcaV3?@`i3kGa5[o\ZEhfQeHEWLoi>7_F6GWU
X-Complaints-To: abuse@sover.net
Xref: g2news2.google.com comp.lang.ada:5415
Date: 2006-07-02T16:08:42+00:00
List-Id: <comp.lang.ada>

Here is what I'm trying to do

generic
  Size : in Integer;
package Xyzzy is
  type Index is mod Size;
  -- etc.
end Xyzzy;

The compiler (gnat) complains about the modular type definition, saying 
that Size is a non-static expression and that's no good. I understand 
what this error means and I understand the rationale behind it (thanks 
to looking in Cohen's book "Ada As a Second Language"). My question is: 
how can I get the effect I'm looking for? My plan is to only instantiate 
the package with constants so all the necessary information should be 
available at compile time. For example

    	package Fizzle is new Xyzzy(Size => 10);

I realize that I could make the Index type a generic parameter but that 
would require me to define the type at the point of instantiation and 
that seems unnatural. Conceptually I'm trying to parameterize the 
package on a (static) size. It doesn't seem like I should have to define 
a type to express that concept.

I admit that I'm a C++ programmer and I'm used to using non-type 
parameters in templates to obtain this effect.

template< int size >
class Xyzzy {
  char array[size];  // size is a compile time constant.
};

Peter