Because of how we find plugins, no plugins are available when running in ``taint'' mode.
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.
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.
Data::Compare::Plugins::Scalar::Properties