I'm building a class that will take a set of iterators and iterate over the combined output, merging records where appropriate. The client passes in a list of iterators and a comparison function for the expected records from the iterators. The iterators are assumed to be returning their values in some sorted fashion.

The problem I'm having is summarized as so:

  1. The iterators are destructive.
  2. Because they're destructive, I need to cache the values that aren't used in a given iteration for use in the next one.
  3. For those iterators that I do use the value this iteration, I need to remove the value in the cache for those iterators. This is so I can get the next value during the next iteration.
  4. The sorting routine (as I've defined it thus far) is expected to accept two records and return -1, 0, or 1 (as appropriate)
  5. But, how do I do something like my @indices = sort $sort_routine 0 .. $#records; when $sort_routine is expecting records, not indices?

The cache is a parallel array of records, each index corresponding to an iterator in @iterators. So, I could do something like: 

RECORD:
for my $record (@merged_records)
{
    my $index;
    for $index (0 .. $#cache)
    {
        if ($cache[$index] eq $record)
        {
            $cache[$index] = 0;
            next RECORD;
        }
    }

    die "Cannot find record to remove in cache!\n";
}

[download]

But, that depends on stringifying the references, and I'm not comfortable with that. Plus, the iterators might not be returning references, so this would fail.

Help!

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In reply to Sorting for indices and client-defined routines by dragonchild

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