Data::Compare::PluginsUser Contributed Perl DocumentaData::Compare::Plugins(3)NAMEData::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.
perl v5.14.2 2009-03-07 Data::Compare::Plugins(3)