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From: "Mattias Lundstr�m" <ehsmalu@ehpt.com>
Subject: Re: Software landmines (loops)
Date: 1998/08/31
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Date: 1998-08-31T00:00:00+00:00
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Andrew Hussey wrote:
> 
> In <m3af4mq7f4.fsf@mheaney.ni.net> Matthew Heaney <matthew_heaney@acm.org> writes:

> >Using an exit from the middle avoids the headaches (literally)
> >engendered by using an extra flag in the predicate.  When you want to
> >exit, you just say that you want to exit, directly.  No mental
> >gymnastics are required in order to determine whether you'll "really"
> >exit, as would be the case using the flag approach.
> 
> That's brilliant, now your code is much easier to write!
> Now let's see who has an easier time *testing* their code.
> I think you'll find the control-flow errors you introduce
> in the spaghetti you produce will more than make up for
> any gain you have from rapid coding.

I just have to butt in here.
Why would this code become harder to test?

If we take a simple example (more or less C++)

1. Flag solution
while( ... && retval == OK ) {
...
if( ... )
  retval = NOT_OK;
}
return retval;

vs

2. Multiple exits
while( ... ) {
...
if( ... )
  return NOT_OK;
}
return OK;

the control flow is basically the same (the same number
of paths functionally identical) so the number and nature 
of tests that are needed have not been affected.

Personally I prefer the second version in many cases
since I believe it is normally easier to write as well
as understand. (Specifically the exceptional exits are 
handled in this way (with return codes) in our projects).

(Ie The maintenance argument - that the second code version
becomes harder to read and understand (and thus maintain) -
since the return statement may well not be obvious if there
is a lot of other code within the loop. I do not agree 
with this, but it is certainly an argument worth considering.
IMHO This should be covered by good comments where applicable.)

- Mattias