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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: type definition for an integer with discrete range
Date: Fri, 29 Mar 2019 21:24:53 +0000
Organization: A noiseless patient Spider
Message-ID: <lylg0x2x22.fsf@pushface.org>
References: <b572b336-e634-48b8-99cd-f987bd5ab12e@googlegroups.com>
	<36c2ff61-8cca-4435-995f-dfc34fa44b69@googlegroups.com>
	<lypnq92zui.fsf@pushface.org>
	<511923fb-dbb9-4e33-82a8-b4bbbf002a6d@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: reader02.eternal-september.org;
 posting-host="d3edd0845bf91e08b6bbdb3ecf0226de";
	logging-data="29595"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX18Xz7R8oan3cf0wCChkLNdaqvL6Ryma+kQ="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (darwin)
Cancel-Lock: sha1:ww2EJ2J2SBniToy2dbaOR9jn2P8=
	sha1:a1Ka4kA+4L0xZj5gkkB21Dt2mxA=
Xref: reader01.eternal-september.org comp.lang.ada:56006
Date: 2019-03-29T21:24:53+00:00
List-Id: <comp.lang.ada>

mario.blunk.gplus@gmail.com writes:

> On Friday, March 29, 2019 at 9:24:38 PM UTC+1, Simon Wright wrote:
>> tra.....g@gmail.com writes:
>> 
>> > On Friday, March 29, 2019 at 11:10:42 PM UTC+7, mario.b...@gmail.com wrote:
>> >> Hello,
>> >> I'm looking for a way to define a type that runs from let say -100
>> >> to +100 with gaps of 5 width. Important is to make sure that a value
>> >> like 7 can not be assigned to the type.
>> >>
>> >> something like:
>> >>
>> >> type number is new integer range -100 .. 100;
>> >> -- or
>> >> subtype number is integer range -100 .. 100;
>> >>
>> >> -- with this special thing or something like that:
>> >> for number'small use 5; -- can not applied here. works with fixed
>> >> point types only
>> >>
>> >> Thanks !
[...]
>>   Number_Small : constant := 5.0;
>>   type Number is delta Number_Small range -100.0 .. 100.0;
>>   for Number'Small use Number_Small;
>
> The problem is that you can assign a variable of type Number 101.0
> without getting a compile error. I wrote a test program at
> https://github.com/Blunk-electronic/ada_training/blob/master/src/type_angle/type_angle.adb
> where the issue can be tested by yourself. Thanks !

If you compile with -gnatwa the compiler says

   type_angle.adb:11:22: warning: static fixed-point value is not a multiple of Small
   type_angle.adb:14:13: warning: static fixed-point value is not a multiple of Small
   type_angle.adb:18:13: warning: value not in range of type "Number" defined at line 8
   type_angle.adb:18:13: warning: "Constraint_Error" will be raised at run time

Changing your 101.0 to 104.9 gives the same result. Printing the "101.0"
value gives 100.0 - so the constraint hasn't been violated.

What about this?

   pragma Assertion_Policy (Check);
   with Ada.Text_Io; use Ada.Text_Io;
   procedure Type_Integer is
      subtype Number is Integer range -100 .. 100
      with Dynamic_Predicate => Number mod 5 = 0;
      V : Number;
   begin
      V := 0;
      Put_Line ("0'image is " & V'Image);
      V := -50;
      Put_Line ("-50'image is " & V'Image);
      V := 42;
      Put_Line ("42'image is " & V'Image);
   end Type_Integer;

Executing gives

   $ ./type_integer 
   0'image is  0
   -50'image is -50

   raised SYSTEM.ASSERTIONS.ASSERT_FAILURE : Dynamic_Predicate failed at
   type_integer.adb:12