http://www.perlmonks.org?node_id=1000626


in reply to Unusual sorting requirements; comparing three implementations.

keysort is an XS implementation of the Schwartzian transform
Well, not really. It is more like this: 
sub sortkey (\&@) {
  my $calc_key = shift;
  my @key = map $calc_key->(), @_;
  return @_[sort { $key[$a] cmp $key[$b] } 0..$#_];
}

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In Section Meditations