Re: GOTO considered Satanic (was: Is there an ADA analogue to the C++ continue statement?)

[eachus@spectre.mitre.org (Robert I. Eachus)]

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

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