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From: Mart van de Wege <mvdwege@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: stopping a loop iteration without exiting it
Date: Fri, 05 Jan 2018 15:35:50 +0100
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Date: 2018-01-05T15:35:50+01:00
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"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:

> On 01/04/2018 10:52 PM, Mart van de Wege wrote:
>> "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:
>>>
>>> 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>
>
> I hardly think Perl is a good example for Ada language design
> decisions.

That answer is a bit parochial.

And you're moving the goalposts. No matter how messy Perl is as a
language, it is being used in the real world, and the use case of
processing a stream of discrete elements is not particularly rare.

The idiom is in common use, even if it is not in a language to your
liking, so your 'never seen a real-world situation' remark is simply not
true.

> This appears to be exactly an example that can be replaced
> by an if statement, anyway.

Creating an unnecessary extra block, making code less readable. And what
of the situation where you want to test for more than one exceptional
situation before handing over your input to the main body of the loop?
You want nested ifs?

In my opinion a 'continue' construct is a useful bit of syntactic sugar
that makes adding guard clauses to a loop easy and obvious to the reader
of the code.

It is by no means *necessary*. A goto statement works just the same.

(As an aside, could it not be implemented using Pre- and
Post-Conditions, just as in subprograms?)

Mart

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