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=encoding utf8

=head1 NAME

Lucy::Search::Matcher - Match a set of document ids.

=head1 SYNOPSIS

    # abstract base class

=head1 DESCRIPTION

A Matcher iterates over a set of ascending document ids.  Some Matchers
implement L<score()|/score> and can assign relevance scores to the docs that they
match.  Other implementations may be match-only.

=head1 CONSTRUCTORS

=head2 new

    my $matcher = MyMatcher->SUPER::new;

Abstract constructor.

=head1 ABSTRACT METHODS

=head2 next

    my $int = $matcher->next();

Proceed to the next doc id.

Returns: A positive doc id, or 0 once the iterator is exhausted.

=head2 get_doc_id

    my $int = $matcher->get_doc_id();

Return the current doc id.  Valid only after a successful call to
L<next()|/next> or L<advance()|/advance> and must not be called otherwise.

=head2 score

    my $float = $matcher->score();

Return the score of the current document.

Only Matchers which are used for scored search need implement L<score()|/score>.

=head1 METHODS

=head2 advance

    my $int = $matcher->advance($target);

Advance the iterator to the first doc id greater than or equal to
C<target>. The default implementation simply calls L<next()|/next>
over and over, but subclasses have the option of doing something more
efficient.

=over

=item *

B<target> - A positive doc id, which must be greater than the current
doc id once the iterator has been initialized.

=back

Returns: A positive doc id, or 0 once the iterator is exhausted.

=head1 INHERITANCE

Lucy::Search::Matcher isa Clownfish::Obj.

=cut