http://www.perlmonks.org?node_id=248871

One problem with making datastructure in Perl that are a little bit more advanced than searching for exact queries, is that it's hard to parameterize the compare function. Suppose you want to create a search tree. What kind of keys are you going to store? Numbers? Strings? But to compare them, you need different operators. And when dealing with data structures, you'll do lots of comparisons.

I know of three solutions to solve this problem:

Below is a benchmark that compares the first and third options, for heapsort. It shows the eval option to be a winner.

Abigail

#!/usr/bin/perl use strict; use warnings; use Benchmark; my @heap; my $M = @ARGV ? shift : 1000; sub heapify; sub heapify { my ($idx, $cmp) = splice @_ => 0, 2; my $max = $idx; for my $try (2 * $idx + 1, 2 * $idx + 2) { $max = $try if $try < @heap && $cmp -> ($heap [$try], $heap [$ +max]); } return if $max == $idx; @heap [$idx, $max] = @heap [$max, $idx]; heapify $max, $cmp; } sub extract { return unless @heap; my $cmp = shift; my $min = $heap [0]; my $tmp = pop @heap; if (@heap) { $heap [0] = $tmp; heapify 0, $cmp; } return $min; } sub heapsort_cmp (&@) { (my ($cmp), @heap) = @_; for (my $i = int (@heap / 2); $i --;) { heapify $i => $cmp; } my @result; push @result => extract $cmp while @heap; @result; } my %cache; sub heapsort_eval ($@) { (my ($cmp), @heap) = @_; unless ($cache {$cmp}) { $cache {$cmp} = 1 + keys %cache; my $sub_heapify = "heapify_$cache{$cmp}"; my $sub_extract = "extract_$cache{$cmp}"; eval <<" --"; sub $sub_heapify; sub $sub_heapify { my (\$idx) = shift; my \$max = \$idx; for my \$try (2 * \$idx + 1, 2 * \$idx + 2) { \$max = \$try if \$try < \@heap && \$heap [\$try] $cmp \$heap [\$max]; } return if \$max == \$idx; \@heap [\$idx, \$max] = \@heap [\$max, \$idx]; $sub_heapify \$max; } sub $sub_extract { return unless \@heap; my \$min = \$heap [0]; my \$tmp = pop \@heap; if (\@heap) { \$heap [0] = \$tmp; $sub_heapify 0; } return \$min; } -- if ($@) {die "eval failed: $@\n"} } no strict 'refs'; my $sub_heapify = "heapify_$cache{$cmp}"; my $sub_extract = "extract_$cache{$cmp}"; for (my $i = int (@heap / 2); $i --;) { &$sub_heapify ($i); } my @result; push @result => &$sub_extract ($cmp) while @heap; @result; } our @data = 1 .. $M; for (my $i = @data; $i --;) { my $r = rand @data; @data [$r, $i] = @data [$i, $r]; } timethese -10 => { cmp => 'heapsort_cmp {$_ [0] < $_ [1]} @::data', eval => 'heapsort_eval "<", @::data' }; __END__ Benchmark: running cmp, eval for at least 10 CPU seconds... cmp: 11 wallclock secs (10.20 usr + 0.01 sys = 10.21 CPU) @ 3.23/ +s (n=33) eval: 11 wallclock secs (10.19 usr + 0.00 sys = 10.19 CPU) @ 4.61/ +s (n=47)