NAME

       Data::Compare::Plugins - how to extend Data::Compare

DESCRIPTION

       Data::Compare natively handles several built-in data types - scalars, references to
       scalars, references to arrays, references to hashes, references to subroutines, compiled
       regular expressions, and globs.  For objects, it tries to Do The Right Thing and compares
       the underlying data type.  However, this is not always what you want.  This is especially
       true if you have complex objects which overload stringification and/or numification.

       Hence we allow for plugins.

FINDING PLUGINS

       Data::Compare will try to load any module installed on your system under the various
       @INC/Data/Compare/Plugins/ directories.  If there is a problem loading any of them, an
       appropriate warning will be issued.

       Because of how we find plugins, no plugins are available when running in "taint" mode.

WRITING PLUGINS

       Internally, plugins are "require"d into Data::Compare.  This means that they need to
       evaluate to true.  We make use of that true value.  Where normally you just put:

           1;

       at the end of an included file, you should instead ensure that you return a reference to
       an array.  This is treated as being true so satisfies perl, and is a damned sight more
       useful.

       Inside that array should be either a description of what this plugin is to do, or
       references to several arrays containing such descriptions.  A description consists of two
       or three items.  First a string telling us what the first data-type handled by your plugin
       is.  Second, (and optional, defaulting to the same as the first) the second data-type to
       compare.  To handle comparisons to ordinary scalars, give the empty string for the data-
       type, ie:

           ['MyType', '', sub { ...}]

       Third and last, we need a reference to the subroutine which does the comparison.  That
       subroutine should expect to take two parameters, which will be of the specified type.  It
       should return 1 if they compare the same, or 0 if they compare different.

       Be aware that while you might give a description like:

           ['Type1', 'Type2', sub { ... }]

       this will handle both comparing Type1 to Type2, and comparing Type2 to Type1.  ie,
       comparison is commutative.

       If you want to use Data::Compare's own comparison function from within your handler (to,
       for example, compare a data structure that you have stored somewhere in your object) then
       you will need to call it as Data::Compare::Compare.  However, you must be careful to avoid
       infinite recursion by calling D::C::Compare which in turn calls back to your handler.

       The name of your plugins does not matter, only that it lives in one of those directories.
       Of course, giving it a sensible name means that the usual installation mechanisms will put
       it in the right place, and meaningful names will make it easier to debug your code.

       For an example, look at the plugin that handles Scalar::Properties objects, which is
       distributed with Data::Compare.

DISTRIBUTION

       Provided that the above rules are followed I see no reason for you to not upload your
       plugin to the CPAN yourself.  You will need to make Data::Compare a pre-requisite, so that
       the CPAN.pm installer does the right thing.

       Alternatively, if you would prefer me to roll your plugin in with the Data::Compare
       distribution, I'd be happy to do so provided that the code is clear and well-commented,
       and that you include tests and documentation.

SEE ALSO

       Data::Compare

       Data::Compare::Plugins::Scalar::Properties

AUTHOR

       Copyright (c) 2004 David Cantrell <david@cantrell.org.uk>.  All rights reserved.  This
       program is free software; you can redistribute it and/or modify it under the same terms as
       Perl itself.