RE: In case statment? (was Re: is exception when others => null; smart?)

["Steven Deller" <deller@smsail.com>]

Peter,
I'd bet it also depends on optimization.  At least for Rational, using
the "for" clauses is tantamount to saying "I know the values at this
location are ok, so just use them".  A 'valid could be used to test, but
otherwise, Rational opts to not test.  And the "when others" is, as
expected, a last ditch if the first two compares fail.

You might change your code to do something like:
  c : boolean
...
begin
   begin
     c := b ;
   exception
     when others => text_io.put_line "yet another possibility" ;
   end ;
   case b is
...

And you might test at different optimization levels.  At level 0,
Rational may very well include a constraint check on b that is, at
higher optimizations, optimized away per RM permissions.

Regards,
Steve
   

> -----Original Message-----

> As the following example illustrates, it really depends upon 
> the compiler too. A "bad" value is handled differently as
> shown:
> -----------------------------------------------------------
> with system;
> with text_io;
> procedure test is
>     
>      a : character := character'val(2#11111111#);   
>      for a'size use 8;
>      b : boolean;
>      for b'address use a'address;
>      for b'size use 8;
>      
> begin 
> 
>    case b is
>       when true =>
>         text_io.put_line ("b is true");     
>       when false =>
>         text_io.put_line ("b is false");
>       when others =>
>         text_io.put_line ("ObjectAda for Windows V7.1.105 "    & 
>                           "professional " edition gets here, " &
>                           "and so does Rational Apex Ada 95 
> v. 4.0.0b");    
>    end case;
>      
> exception
>    when others =>  
>       text_io.put_line ("Gnat 3.14P gets here ");  
> end test;
>