Re: stopping a loop iteration without exiting it

[Mart van de Wege <mvdwege@gmail.com>]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:

> On 01/04/2018 12:17 AM, Robert A Duff wrote:
>>
>> 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.
>
> I have never seen a real-world situation in which a "continue" was
> needed.

It's a common idiom in Perl when looping over a stream of discrete items
(like lines in a file). A test at the top of the loop for cases where
processing is not necessary in the form of

  next if <condition>

(a popular one is in file processing, to skip comment lines:

  next if /^#/;

aka, skip this line if it starts with a # character indicating a
comment)

Since these are basically guard clauses, the idiom is clear to anyone
with more than a cursory knowledge of the language (and anyone
pretending to be a programmer, let alone a software engineer, should be
smart enough to recognise this as the loop equivalent of a guard clause
on a second look).

The resistance against adding a similar construct to Ada is puzzling to
me. It is clear, and more elegant than the more general 'goto' that is
the only way to do this in Ada. Adding a goto with a label at the top of
the loop is not clear until you seek out the label near the 'end loop'
statement; if that is out of sight it may well appear as an attempt to
break out of the loop.

Mart

-- 
"We will need a longer wall when the revolution comes."
--- AJS, quoting an uncertain source.