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=head1 NAME

Lucy::Index::Snapshot - Point-in-time index file list.

=head1 SYNOPSIS

    my $snapshot = Lucy::Index::Snapshot->new;
    $snapshot->read_file( folder => $folder );    # load most recent snapshot
    my $files = $snapshot->list;
    print "$_\n" for @$files;



=head1 DESCRIPTION

A Snapshot is list of index files and folders.  Because index files, once
written, are never modified, a Snapshot defines a point-in-time view of the
data in an index.

L<IndexReader|Lucy::Index::IndexReader> objects interpret the data
associated with a single Snapshot.

=head1 CONSTRUCTORS

=head2 new()

    my $snapshot = Lucy::Index::Snapshot->new;

Constructor.  Takes no arguments.





=head1 METHODS

=head2 list()

Return an array of all entries.

=head2 num_entries()

Return the number of entries (including directories).

=head2 add_entry(entry)

Add a filepath to the snapshot.

=head2 delete_entry(entry)

Delete a filepath from the snapshot.

Returns: true if the entry existed and was successfully deleted, false
otherwise.

=head2 read_file( I<[labeled params]> )

Decode a snapshot file and initialize the object to reflect its
contents.

=over

=item *

B<folder> - A Folder.

=item *

B<path> - The location of the snapshot file.  If not supplied, the
most recent snapshot file in the base directory will be chosen.

=back

Returns: the object, allowing an assignment idiom.

=head2 write_file( I<[labeled params]> )

Write a snapshot file.  The caller must lock the index while this
operation takes place, and the operation will fail if the snapshot file
already exists.

=over

=item *

B<folder> - A Folder.

=item *

B<path> - The path of the file to write.  If undef, a file name will
be chosen which supersedes the latest snapshot file in the index
folder.

=back

=head2 set_path(path)

Set the path to the file that the Snapshot object serves as a proxy
for.

=head2 get_path()

Get the path to the snapshot file.  Initially undef; updated by
read_file(), write_file(), and set_path().



=head1 INHERITANCE

Lucy::Index::Snapshot isa L<Lucy::Object::Obj>.


=cut