Adding an entry for a matched $module

Question

What would be the most efficient way to write the following code in Perl:

 my $index = 0;
 foreach ( @spec ) {
 if ( $module =~ m/$_/ ) {
 splice(@spec, $index, 0, $module);
 last; 
 }
 $index++;
 }

This works fine but just seems a little wordy. The idea is that where I find a match for $module in the array I add an entry. I want to keep the array in a certain order and sorted.

Answer 1

You want "more efficient wordiness"??? I presume you're not asking for golfing, but for code that's more readable from conciseness.

@spec = map { $_ eq $module ? ($_, $_) : $_ } @spec;

• evolution: Yeah this is perfect!

Answer 2

1. You manually increment the $index. Just loop over the indices instead:

   for my $index (0 .. $#spec) {
    if ($module =~ /$spec[$index]/) {
    splice @spec, $index, 0, $module;
    last;
    }
   }
   

   On newer perls (v12+) you can use each on arrays:

   use 5.012;
   while(my ($i, $str) = each @spec) {
    if ($module =~ /$str/) {
    splice @spec, $i, 0, $module;
    keys @spec; # reset the `each` iterator
    last;
    }
   }
   

2. If the values in @spec are not regexes, but just plain strings, and iff you want to test that $module contains the string in $spec[$index], then you could use index for better efficiency.

   if (-1 != index $module, $spec[$index]) { ... }
   

   This also won't treat characters like \[]()?+* as metacharacters any more. This would be similar to /\Q$spec[$index]\E/ (see quotemeta function), but more efficient

   If you actually want to apply the string as a regex, this point is moot.

• Grzegorz Rożniecki: Ad. #1: I'd use foreach loop and increment counter manyally just like OP, so it's rather subjective (although each would be my choice if all production code run on >= v5.12).
• ikegami: It would probably be safer to reset the iterator before you modify the array.