Ryan C. Thompson > List-Flatten-Recursive > List::Flatten::Recursive

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NAME ^

List::Flatten::Recursive - List::Flatten with recursion

VERSION ^

version 0.103460

SYNOPSIS ^

    use List::Flatten::Recursive qw( flat );
    sub printlist { print '(' . join(', ', @_) . ")\n" }

    my $crazy_listref = [ 1, [ 2, 3 ], [ [ [ 4 ] ] ] ];
    my @flattened = flat($crazy_listref); # Yields (1,2,3,4)
    printlist(@flattened);
    push @$crazy_listref, $crazy_listref; # Now it contains itself!
    @flattened = flat($crazy_listref);    # Still yields (1,2,3,4)
    printlist(@flattened);
    @flattened = flat([ $crazy_listref ]); # Ditto.
    printlist(@flattened);
    # But don't do this for self-referential lists.
    @flattened = flat(@$crazy_listref); # Will not yield the same as above.
    printlist(@flattened);

DESCRIPTION ^

If you think of nested lists as a tree structure (an in Lisp, for example), then flat basically returns all the leaf nodes from an inorder tree traversal, and leaves out the internal nodes (i.e. listrefs). If the nested list is a DAG instead of just a tree, it should still flatten correctly (based on my own definition of correctness, of course; see also t/flatten-dag.t).

If the nested list is self-referential, then any cycles will be broken by replacing ancestor references with empty lists. However, the only behavior you should rely on when flattening a self-referential data structure is that infinite recursion should not occur, and each non-list element in the data structure should appear at least once in the output.

METHODS ^

flat

This method flattens a list (or listref) recursively. It takes a list that may contain other sublists, and replaces those sublists with their contents, recursively, until the list no longer contains any sublists.

flat makes a best effort to break circular references (that is, lists that contain references to themselves), so it should not enter infinite recursion. If you find a case that causes it to recurse infinitely, please inform me.

This method is exported by default.

flatten_to_listref

Same as flat, but returns a single reference to the resulting list.

This method is exported only by request. To use this method, put the following at the top of your program:

    use List::Flatten::Recursive qw( flatten_to_listref );

BUGS AND LIMITATIONS ^

Self-referential lists should be flattened by reference

If you are going to flatten a list which might contain references to itself, you should pass a reference to that list to flat, or else things will not work the way you expect. You will end up with an extra instance of each item in the outermost list. However, this will not result in infinite recursion.

This module should never cause infinite recursion. If it does, please submit a bug report.

flat always returns a list

Even if you call flat on a single scalar, it will still return a list with one element in it. If called in scalar context, it will return the length of that list. flatten_to_listref would return a reference to a list with one element. There is no case where the original scalar would be returned directly. This is by design. If you think this is wrong, email me and tell me why.

Please report any bugs or feature requests to rct+perlbug@thompsonclan.org. If you find a case where this module returns what you feel is a wrong result, please send an example that will cause it to do so, along with the actual and expected results.

SEE ALSO ^

* List::Flatten The non-recursive insipiration for this module.

DISCLAIMER OF WARRANTY ^

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

AUTHOR ^

Ryan C. Thompson <rct@thompsonclan.org>

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2010 by Ryan C. Thompson.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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