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=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,8276b2994037cd71
X-Google-Attributes: gid103376,public
From: wayne lydecker <wlydeckr@pacbell.net>
Subject: Re: disjoint ranges ?
Date: 2000/10/13
Message-ID: <39E79F17.24DB0828@pacbell.net>#1/1
X-Deja-AN: 681196837
Content-Transfer-Encoding: 7bit
References: <39E612C9.9BF98CD3@laas.fr>
X-Accept-Language: en
Content-Type: text/plain; charset=us-ascii
X-Complaints-To: abuse@cts.com
X-Trace: thoth.cts.com 971480811 424 63.202.234.84 (13 Oct 2000 23:46:51 GMT)
Organization: CTSnet Internet Services
Mime-Version: 1.0
Newsgroups: comp.lang.ada
Date: 2000-10-13T00:00:00+00:00
List-Id: <comp.lang.ada>

>Philippe Torres wrote:
>
>> A very dumb question but i can't find the right syntax so here i am.
>> How can i declare a type or subtype with a disjoint range ?
>>
>> Example :
>>
>> If i declare :
>> ---
>> type Hours is new Integer range 0 .. 23 ;
>> --
>> i would like a
>> ---
>> subtype Lunch_Hours is Hours range 7..9 & 12..14 & 19..21 ;
>> ---
>
>The problem of disjoint ranges came up for me many years ago on a different
>project.   I
>even suggested this as a capability for Ada 9X, but my suggestion either
>fell through the
>cracks or I submitted it incorrectly.
>
>My first attempt at a solution was to try to overload the "in" test as a
>boolean function.  That
>turns out to be illegal for a variety of reasons that require careful study
>of the language rules
>for the "in" test.   It turns out that membership tests are not
>operations/operators in Ada.
>
>I finally ended up declaring a function that would do this test, but did
>not use operator
>overloading.   It does solve the problem, but requires you call the
>function each place
>you intend to use a value of the type.
>
>A better approach  would probably be to add a capability for assertion
>checking.
>This simple mechanism could be added at the type level or the subprogram
>level
>within the package specification.  The notion of range checks was a good
>one in
>the early design of Ada.   Perhaps the same thing can be accomplished
>through
>assertions in some future version.
>
>Richard Riehle

How about using a boolean array:

with Text_IO;
procedure lunch is
  type Hours is new Integer range 0 .. 23 ;
  Lunch_Hours : array (Hours) of Boolean :=
    (7..9 => True, 12..14 => True, 19..21 => True, others => False);
begin
  if Lunch_Hours(7) then
    text_io.put_line("Lunch time");
  else
    text_io.put_Line("Get back to work");
  end if;
end;


-- Wayne.