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,ec4cde5d799065b6
X-Google-Attributes: gid103376,public
From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: GOTO considered Satanic (was: Is there an ADA analogue to the C++
 continue statement?)
Date: 1997/10/07
Message-ID: <EACHUS.97Oct7162405@spectre.mitre.org>#1/1
X-Deja-AN: 278517281
References: <dewar.874665174@merv> <3422F037.41CA@lmco.com>
 <3423AF1B.5152@i.b.m.net> <6098m7$a24$1@krusty.irvine.com>
 <Pine.SGI.3.95.970924182021.11641A-100000@shellx.best.com>
 <mheaney-ya023680002609970839420001@news.ni.net>
Organization: The Mitre Corp., Bedford, MA.
Newsgroups: comp.lang.ada
Date: 1997-10-07T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <mheaney-ya023680002609970839420001@news.ni.net> mheaney@ni.net (Matthew Heaney) writes:

  > Well, there are reasons for not using exceptions for normal control flow:
  > the famous RM 11.6 (though that section may - I think - only apply to
  > predefined exceptions; that section still throws me).  If you need a goto,
  > then use a goto, not an exception.

  The wording in 11.6(5) in the new RM cleans up this problem almost
completely.  The only case where you can still find yourself fighting
the optimizer is:

   declare
     Junk: Integer;
   begin
     Junk := X * Y;
   exception
     when Constraint_Error => Handle_Value_Too_Big;
   end;

   Since Junk is never referenced, the optimizer is allowed to leave
the value of X * Y undefined, and in fact not compute it.  To do this
type of check correctly try:

   declare
     Junk: Integer;
   begin
     Junk := X * Y;
     if Junk > Integer'LAST 
     then
       Ada.Text_IO.Put_Line("Foo!");
     end if;
   exception
     when Constraint_Error => Handle_Value_Too_Big;
   end;

   The call to Put_Line can never be made, but it prohibits the
optimizer from deciding that the value of Junk has no effect.

--

					Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...