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From: "Chad R. Meiners" <crmeiners@hotmail.com>
Newsgroups: comp.lang.ada
Subject: Implementing an elegant range type.
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Message-ID: <3ab6442f.0@silver.truman.edu>
Date: Mon, 19 Mar 2001 11:45:56 -0600
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Date: 2001-03-19T11:45:56-06:00
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There are certain times that I have wanted to pass ranges as a
parameter to subroutines, for example being able to
write, "Register_Slots (75..4242);" which of course isn't directly
allowed.  The solution I came up with is to declare a null type that
doesn't take up any memory so that I can create array type of the
ranges I want as in the example below.

type Nothing is null record;
for  Nothing'Size use 0;

type Integer_Range_Type is array (Integer range <>) of Nothing;

Thus I could declare an array, "Integer_Range : Integer_Range_Type
(Integer);", and use it to pass array slice which would contain the
range data.  Example: "Register_Slots (Integer_Range(75..4242));"

The problem I am encountering is that when I declare a variable
with a range as large as Integer_Range's I get a
Storage_Error which doesn't make much sense since if Integer_Range's
range is something smaller than 2**20 elements, Integer_Range'Size
equals 8 for all cases which I expect should be true even for the
large cases since the elements of the array have no size.  I am
using GNAT 3.13p on WinNT.

Has anyone used a similar approach for representing ranges or have
any advice on getting around the Storage_Error for large ranges?

Thank you,
-Chad R. Meiners