Re: is exception when others => null; smart?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Per Sandbergs" <prsa@cntw.com> writes:

> 1)
>   main_loop:
>     loop
>       begin
>         lots of operations.
>       exception
>         when others =>
>           report the error and reset top a safe state in order to continue.
>     end loop;
> 
> 2)
> function work_is_ok(fool) return boolean is
> begin
>     some computations
> exception --
>     when others =>
>         return false; -- or report error and eventualt raise.
> end;
> 2)
> procedure must_not_raie(fool) is
> begin
>     some computations
> exception
>     when others =>
>         null;
> end;
> So when others => null is only to be used when you are expecting the
> unexpected.
> I wont be supprised if other peoplen are of different opinion but after
> integration a number of large systems i find the above aproach "wise".

Also,

4)

    when others =>
        clean up;
        raise;

As in:

    procedure Walk_Tree(...) is
    begin
        Push current node on stack;
        walk subtrees;
        Pop stack;
    exception
        when others =>
            Pop stack; -- Keep stack in synch even in case of exception.
            raise;
    end Walk_Tree;

Finalization can also be used for this purpose, and that's a cleaner way
to do it, but finalization is *very* expensive in most Ada compilers,
whereas the above "when others" is pretty cheap.

- Bob