Re: stopping a loop iteration without exiting it

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

"Randy Brukardt" <randy@rrsoftware.com> writes:

> A "goto" is *not* stupid in this case.

I agree.  There are (rare) cases in Ada when "goto" is the right
solution, and nested "continue" can be one of them.

I've even heard the argument that "Goto CAN always be replaced by
if/while/etc" (proved by Jacopini in the 60's, IIRC), that therefore
"Goto SHOULD always be replaced by if/while/etc".  That "therefore"
is obviously a logical fallacy.

>... It isn't always sensible to 
> restructure a loop to avoid "continue". We looked at adding the feature 
> sometime back (it happens hundreds of times in the GNAT source code), but 
> the decision was that a goto was good enough.

In fact, the goto is BETTER than the continue statement, because the
place where it's jumping to is marked with a label, as in Randy's
example below.  With a "continue", when you see "end loop" (or "}"!)
you have no clue that "something is interesting here -- somebody is
jumping to this place".

Jeff's suggestion (nested 'if' in the loop) is a good one when it works,
but it doesn't work when the "continue" is nested within further control
constructs.

>...(Especially after the syntax 
> change allowing it directly at the end of a loop.) That is:
>
>     loop
>       ...
>              goto Continue;
>       ...
>     <<Continue>>
>     end loop;

And Randy indents the "goto" a lot, to show that it is (perhaps) deeply
nested.  That's exactly when the goto makes good sense.

- Bob