Re^7: loop surprise

[Skeeve]

I can remember that long time (say: 30 or more years) ago, I also wrote loops like that.

But now that you mention it, and thinking about it, I notice always write those kind of loops like:

my $interesting_index= 'not existing';

for ($i=1; $i<=10; ++$i) {
  next unless &condition($i);
  $interesting_index= $i;
  last;
}
# spit an error if $interesting_index is still 'not existing'

The reason behind this is simply that your loop might not have found a valid value.

[Marshall]

There are many variants of how to do this. My inclination might be:

my $interesting_index;
my $i = 0;

while (!defined($interesting_index) and $i++ <= 10)
{   
    $interesting_index = $i if condition($i);
}

# spit an error if $interesting_index is still 'not defined'

If the purpose of the loop is to find an index, then I would try to make that fact prominent at the start of the loop. That way you don't have to read the body of the code to figure out the purpose/intent.

In Perl often there are other ways to do something similar to this functionality with the various List::utils. My Perl code rarely uses any $i subscripts.

update: maybe I have an "off by one" error in original post. I think it is also possible to use the C style loop:

for (my $i=1; !defined($interesting_index) and $i<=10; $i++){}