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=head2  List::Compare

    use List::Compare;              # Compare elements of two or more lists
    # This object-oriented module is highly orthogonal,
    #   so that nearly any selection or choice may be combined with any other.
    # Most methods are equally okay for ( just two ) or ( three or more ) lists;
    #   some will Carp if called inappropriately.
    #                            === Options/Modes ===
    #           Regular: (default) Two lists, sorted results, many method calls ok
    #          Unsorted: Don't sort method results              ( faster )
    #       Accelerated: Only one method call possible per $lc  ( faster )
    #          Multiple: Three or more lists in constructor
    # ! (specify $ix to refer to a given list; default 0; omit for only two lists)
    #         Seen-hash: Use hashrefs instead of arrayrefs:
    #   [ 11, 12, 14, 14, 14, 15 ] ~~ { 11 => 1, 12 => 1, 14 => 3, 15 => 1 }
    #
        # Construct a work-object
        my $lc = List::Compare->new(             \@a, \@b, @c );  # default
        my $lc = List::Compare->new( '-u',       \@a, \@b, @c );  # unsorted
        my $lc = List::Compare->new(       '-a', \@a, \@b, @c );  # accelerated
        my $lc = List::Compare->new( '-u', '-a', \@a, \@b, @c );  #! -u before -a
        # Wrap constructor arguments in a hashref
        my $lc = List::Compare->new({
            unsorted    => 1,
            accelerated => 1,
            lists       => [ \@a, \@b, @c ],
        });
        # Methods return lists of results
        @gots = $lc->get_intersection;          # found in each/both list(s)
        @gots = $lc->get_union;                 # found in any/either list
        @gots = $lc->get_bag;                   # ~get_union but also duplicates
        @gots = $lc->get_unique($ix);           # found only in list $ix
        @gots = $lc->get_complement($ix);       # not found in $ix, but elsewhere
        @gots = $lc->get_symmetric_difference;  # found in only one list
        $gots = $lc->get_intersection_ref;          # ~methods above but
        $gots = $lc->get_union_ref;                 #           returns \@gots
        $gots = $lc->get_bag_ref;                   #       "
        $gots = $lc->get_unique_ref($ix);           #       "
        $gots = $lc->get_complement_ref($ix);       #       "
        $gots = $lc->get_symmetric_difference_ref;  #       "
        # Methods return boolean truth      # ( $ixL, $ixR ) default to ( 0, 1 )
        $bool = $lc->is_LsubsetR( $ixL, $ixR );     # true if all L in R
        $bool = $lc->is_RsubsetL( $ixL, $ixR );     # true if all R in L
        $bool = $lc->is_LequivalentR( $ixL, $ixR ); # true if same items in L, R
        $bool = $lc->is_LdisjointR( $ixL, $ixR );   # true if no items in common
        # Methods return list of which lists ($ix) satisfying conditions
        @ixs  = $lc->is_member_which($string);      # some item in $ix eq $string
        @ixs  = $lc->are_members_which(\@strings);  # ~prev but eq any in @strings
        # Dump
        $lc->print_subset_chart;        # pretty-print tables showing some
        $lc->print_equivalence_chart;   #   relationships; row/col as $ix
    # List::Compare

=head2  Hash::Util

    use Hash::Util;                 # Hash locking, key locking, value locking
    use Hash::Util qw(
        lock_keys lock_keys_plus unlock_keys
        lock_value unlock_value
        lock_hash unlock_hash lock_hash_recurse unlock_hash_recurse
        hash_locked hidden_keys legal_keys all_keys
    );
        # Restrict %hash to a set of keys; can delete but can't add other keys
        \%hash = lock_keys     ( %hash );           # current keys %hash
        \%hash = lock_keys     ( %hash, @keys );    # @keys; subset of keys @hash
        \%hash = lock_keys_plus( %hash, @keys );    #        superset
        \%hash = unlock_keys   ( %hash );           # remove restrictions
        # Cannot alter value of $key but can delete the k/v pair
        \%hash = lock_value    ( %hash, $key );
        \%hash = unlock_value  ( %hash, $key );
        # Lock the whole %hash; can't add, delete, or change value at all
        \%hash = lock_hash              ( %hash );
        \%hash = unlock_hash            ( %hash );
        \%hash = lock_hash_recurse      ( %hash );  # HoHoH... only
        \%hash = unlock_hash_recurse    ( %hash );  #   ditto
        # Other functions...
        $bool  = hash_unlocked ( %hash );       # true if %hash is unlocked
        @keys  = legal_keys    ( %hash );       # list of keys allowed
        @keys  = hidden_keys   ( %hash );       # see docs; experimental feature
        \%hash = all_keys( %hash, @keys, @hidden );       # experimental feature
        # Just like Daddy but take hashref arguments
        \%hash = lock_ref_keys          ( \%hash );
        \%hash = lock_ref_keys          ( \%hash, @keys );
        \%hash = lock_ref_keys_plus     ( \%hash, @keys );
        \%hash = unlock_ref_keys        ( \%hash );
        \%hash = lock_ref_value         ( \%hash, $key );
        \%hash = unlock_ref_value       ( \%hash, $key );
        \%hash = lock_hashref           ( \%hash );
        \%hash = unlock_hashref         ( \%hash );
        \%hash = lock_hashref_recurse   ( \%hash );
        \%hash = unlock_hashref_recurse ( \%hash );
        $bool  = hash_ref_unlocked      ( \%hash );
        @keys  = legal_ref_keys         ( \%hash );
        @keys  = hidden_ref_keys        ( \%hash );
    ## Hash::Util

=head1 SEE ALSO

=over

=item * L<Cheat::Meta>

=item * L<perlcheat>

=back

=head1 FUNCTIONS/METHODS

None. This module contains only POD. Don't try to load it. 

=head1 INTERFACE 

Open the cheat (the *.perl file) in your editor. 
Copy out whatever you like. 

If you look at the *.pod file, you'll see POD verbatim paragraphs.
Your choice. 

You can also get the same content in your pager with: 

    perldoc Cheat::Sheet::Util

=head1 BUGS AND LIMITATIONS

No cheat sheet will teach you anything. It's only a reminder. You B<must> 
consult each module's own full documentation I<at least> before using it. 
I hope. 

This module does not contain magic to squirt code into your module. 
Copy and paste. 

No boilerplate code will work right away. Edit it to your needs. 

=head1 THANKS

=over

=item *

To about 8500 authors who have uploaded about 85,000 modules to the CPAN. 

=back

=head1 AUTHOR

Xiong Changnian  C<< <xiong@cpan.org> >>

=head1 LICENSE

Copyright (C) 2010 Xiong Changnian C<< <xiong@cpan.org> >>

This library and its contents are released under Artistic License 2.0: