Re: Exit Do

Anthony Jones wrote:
Robbie Flower wrote:

I've been instructed by a dot net / asp programmer that Exit Do is
not a great way to end a loop.

Can someone explain to me if this is so, or does this only apply to
higher level programming languages ?

I am using nested loops and need to exit out of one loop into
another for something to apply. Any other functional ways of doing
this ?


As with all things its best to consider sticking with good sound
principles rather than making rules. Exit Do/For/Function/Sub has
its uses but it also has its abuses.

Indescriminate use of Exits can make it difficult to determine under
what conditions a particular block of code will end early. Also use
of Exits can make code more difficult to modify and/or lead to bugs
later on.

For example:-

Begin enumerating items
Do Until finished enumeration items
Code stage A
If Some Reason to stop loop then Exit Do
Code Stage B
Loop

In this code stage B is not be executed if there is a reason to exit
the loop. What happens if a developer comes along 6 months later and
adds some code to the loop prior to stage A that allocates a resource
that needs to be expicitly released? It could be easy to miss the
exit do in the existing code and simply add the releasing code after
stage B. That would be a bug.

On the other you can find yourself jumping through all sorts of hoops
trying to get execution of a loop to the end of the construct in
order to avoid using an Exit. In which case this is also just as
likely to lead to bugs and readability problems.

Therefore I would avoid Exits if the loop remains reasonably
readable. If Exits are needed make them really, really obvious.

A good example where Exits would be useful, even expected, is in a
search loop. The loop enumerates a set so it will end when the set
is consumed. However it is expected that once a specific item is
found it will end there and then. These loops tend to be simple and
the presence of the exit is obvious.

Unfortunatly, your reason/example is too vague to provide any worthwhile
value. A developer who comes along 6 months later and introduces a bug by
making modifications is the direct cause of the bug, not the original
developers' EXIT usage which worked properly prior to modifications.

IMO, what you have described above is an unjustified excuse to blame a
previous developer for incompetent modifications.

'Modification 6 months later (as described above)
Begin enumerating items
Do Until finished enumeration items
Modification requiring a resource release
Code stage A
If Some Reason to stop loop then
Modification to release resource
Exit Do
End If
Code Stage B
Loop

--
Todd Vargo
(Post questions to group only. Remove "z" to email personal messages)

.

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