i agree that footpad has nothing to worry about here. however, i think the hash solution that makes sense isn't the one you argued against.

there's a hash solution that makes sense if three things are true:

1. you're finding indices in this list fairly often
2. you're changing the array fairly rarely
3. you have no repeats or a simple decision making process about what to do with them.

what do i mean by "fairly" often and "fairly" frequently? i think probably if you are looking up 3 for each change you make to the array, and you can capture all array changes, then this is a good solution. as for #3, i'll assume you always want the 1st occurence.

the idea is, basically, to construct a lookup hash where for any $array[$i] == $value, there's $lookup{$value} == $i. for instance, you might write it this way:

{
 my %lookup;
 
 sub _init_lookup_hash {
   %lookup;
   for my $i (0..$#_) {
     $lookup{$_[$i]} = $i unless defined $lookup{$_[$i]};
   }
 }

 sub list_index { return $lookup{$_[0]} or -1 } ;
}
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