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package Text::Match::FastAlternatives;
use strict;
use warnings;
our $VERSION = '0.02';
use base qw<DynaLoader>;
__PACKAGE__->bootstrap($VERSION);
1;
__END__
HideShow 117 lines of Pod
=head1 NAME
Text::Match::FastAlternatives - efficient search for many strings
=head1 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);
    }
=head1 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: the keys may not contain
any control characters or non-ASCII characters; and it cannot do
case-insensitive matching.  If you want case-insensitivity, 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,
Regexp::Trie produced a regex that ran 857% faster than the naive regex
(according to L<Benchmark>), but using Text::Match::FastAlternatives ran 18275%
faster than the naive regex, or twenty times faster than Regexp::Trie's
optimised regex.
=head1 METHODS
=over 4
=item 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, or if any of
them contain any control characters or non-ASCII characters.
=item $matcher->match($target)
Returns a boolean value indicating whether the $target string contains any of
the keys in $matcher.
=back
=head1 CAVEATS
=head2 Subclassing
Text::Match::FastAlternatives has a C<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.
=head2 Perl 5.10
Perl 5.10 will contain many enhancements to the regex engine, including
built-in optimisations for regexes with many branches that contain only literal
strings.  I suspect that, for the cases where Text::Match::FastAlternatives is
currently very fast, it will also be faster than Perl 5.10's regex engine.  But
I may be wrong; if you're using Perl 5.9.4 or newer, you'd be well advised to
compare the available options on data sets you're likely to use in practice.
=head1 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(I<mn>) where I<m> is the length of the target string and I<n>
is the length of the longest key.
=head1 SEE ALSO
L<http://en.wikipedia.org/wiki/Trie>, L<Regexp::Trie>, L<Regexp::Optimizer>,
L<Regexp::Assemble>, L<perl594delta>.
=head1 AUTHOR
Aaron Crane E<lt>arc@cpan.orgE<gt>
=head1 COPYRIGHT
Copyright 2006 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.
=cut