NAME Text::Match::FastAlternatives - efficient search for many strings SYNOPSIS use Text::Match::FastAlternatives; my $expletives = Text::Match::FastAlternatives->new(@naughty); while (my $line = <>) { print "Do you email your mother with that keyboard?\n" if $expletives->match($line); } DESCRIPTION This module allows you to search for any of a list of substrings ("keys") in a larger string. It is particularly efficient when the set of keys is large. This efficiency comes at the cost of some flexibility: if you want case-insensitive matching, you have to fold case yourself: my $expletives = Text::Match::FastAlternatives->new( map { lc } @naughty); while (my $line = <>) { print "Do you email your mother with that keyboard?\n" if $expletives->match(lc $line); } This module is designed as a drop-in replacement for Perl code of the following form: my $expletives_regex = join '|', map { quotemeta } @naughty; $expletives_regex = qr/$expletives_regex/; while (my $line = <>) { print "Do you email your mother with that keyboard?\n" if $line =~ $expletives_regex; } Text::Match::FastAlternatives can easily perform this test a hundred times faster than the equivalent regex, if you have enough keys. The more keys it searches for, the faster it gets compared to the regex. Modules like Regexp::Trie can build an optimised version of such a regex, designed to take advantage of the niceties of perl's regex engine. With a large number of keys, this module will substantially outperform even an optimised regex like that. In one real-world situation with 339 keys, running on Perl 5.8, Regexp::Trie produced a regex that ran 857% faster than the naive regex (according to Benchmark), but using Text::Match::FastAlternatives ran 18275% faster than the naive regex, or twenty times faster than Regexp::Trie's optimised regex. The enhancements to the regex engine in Perl 5.10 include algorithms similar to those in Text::Match::FastAlternatives. However, even with very small sets of keys, Perl has to do extra work to be fully general, so Text::Match::FastAlternatives is still faster. The difference is greater for larger sets of keys. For one test with only 5 keys, Text::Match::FastAlternatives was 21% faster than perl-5.10.0; with 339 keys (as before), the difference was 111% (that is, slightly over twice as fast). METHODS Text::Match::FastAlternatives->new(@keys) Constructs a matcher that can efficiently search for all of the @keys in parallel. Throws an exception if any of the keys are undefined. $matcher->match($target) Returns a boolean value indicating whether the $target string contains any of the keys in $matcher. $matcher->match_at($target, $pos) Returns a boolean value indicating whether the $target string contains any of the keys in $matcher at position $pos. Returns false (without emitting any warning) if $pos is larger than the length of $string. $matcher->exact_match($target) Returns a boolean value indicating whether the $target string is exactly equal to any of the keys in $matcher. CAVEATS Subclassing Text::Match::FastAlternatives has a "DESTROY" method implemented in XS. If you write a subclass with its own destructor, you will need to invoke the base destructor, or you will leak memory. Interaction with Perl internals Text::Match::FastAlternatives may change the Perl-internal encoding of strings passed to "new" or to its "match" methods. This is not considered a bug, as the Perl-internal encoding of a string is not normally of interest to Perl code (as opposed to Perl internals). However, you may encounter situations where preserving a string's existing encoding is important (perhaps to work around a bug in some other module). If so, you may need to copy scalar variables before matching them: $matches++ if $tmfa->match(my $temporary_copy = $original); IMPLEMENTATION Text::Match::FastAlternatives manages to be so fast by using a trie internally. The time to find a match at a given position in the string (or determine that there is no match) is independent of the number of keys being sought; worst-case match time is linear in the length of the longest key. Since a match must be attempted at each position in the target string, total worst-case search time is O(*mn*) where *m* is the length of the target string and *n* is the length of the longest key. The "match_at" and "exact_match" methods only need to find a match at one position, so they have worst-case running time of O(min(*n*, *m*)). SEE ALSO , Regexp::Trie, Regexp::Optimizer, Regexp::Assemble, perl5100delta, perlunitut, perlunifaq. AUTHOR Aaron Crane COPYRIGHT Copyright 2006, 2007, 2008 Aaron Crane. This library is free software; you can redistribute it and/or modify it under the terms of the Artistic License, or (at your option) under the terms of the GNU General Public License version 2.