The ordered hash structure uses three things: Thus: 
$orderedhash{$newkey} = $newvalue;
# is really doing

  $next_index = @KEYS;
  $KEYINDEX{$key} = $next_index;
  push @KEYS, $key;
  push @VALUES, $value;

$orderedhash{$oldkey} = $newvalue;
# is really doing

  $key_index = $KEYINDEX{$key};
  $VALUES[$key_index] = $value;

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Deletions require splicing the two arrays, and then lowering the values in the %KEYINDEX hash. And if you want to allow for in-the-middle insertion, that requires splicing again, and raising the values in the hash.

This is obviously a slow structure and a slow process. It does not make for optimization. Hashes are designed so that keys can be looked up quickly, and Perl's hash structure might change soon to make Perl realize that a non-existent key isn't in the hash sooner (that's good).

$_="goto+F.print+chop;\n=yhpaj";F1:eval

In reply to Re: Hash Internals by japhy
in thread Hash Internals by orthanc

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