1Data::Compare::Plugins(U3s)er Contributed Perl DocumentatDiaotna::Compare::Plugins(3)
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6 Data::Compare::Plugins - how to extend Data::Compare
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9 Data::Compare natively handles several built-in data types - scalars,
10 references to scalars, references to arrays, references to hashes,
11 references to subroutines, compiled regular expressions, and globs.
12 For objects, it tries to Do The Right Thing and compares the underlying
13 data type. However, this is not always what you want. This is
14 especially true if you have complex objects which overload
15 stringification and/or numification.
16 Hence we allow for plugins.
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20 Data::Compare will try to load any module installed on your system
21 under the various @INC/Data/Compare/Plugins/ directories. If there is
22 a problem loading any of them, an appropriate warning will be issued.
23 Because of how we find plugins, no plugins are available when running
25 in "taint" mode.
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28 Internally, plugins are "require"d into Data::Compare. This means that
29 they need to evaluate to true. We make use of that true value. Where
30 normally you just put:
31 1;
33 at the end of an included file, you should instead ensure that you
35 return a reference to an array. This is treated as being true so
36 satisfies perl, and is a damned sight more useful.
37 Inside that array should be either a description of what this plugin is
39 to do, or references to several arrays containing such descriptions. A
40 description consists of two or three items. First a string telling us
41 what the first data-type handled by your plugin is. Second, (and
42 optional, defaulting to the same as the first) the second data-type to
43 compare. To handle comparisons to ordinary scalars, give the empty
44 string for the data-type, ie:
45 ['MyType', '', sub { ...}]
47 Third and last, we need a reference to the subroutine which does the
49 comparison. That subroutine should expect to take two parameters,
50 which will be of the specified type. It should return 1 if they
51 compare the same, or 0 if they compare different.
52 Be aware that while you might give a description like:
54 ['Type1', 'Type2', sub { ... }]
56 this will handle both comparing Type1 to Type2, and comparing Type2 to
58 Type1. ie, comparison is commutative.
59 If you want to use Data::Compare's own comparison function from within
61 your handler (to, for example, compare a data structure that you have
62 stored somewhere in your object) then you will need to call it as
63 Data::Compare::Compare. However, you must be careful to avoid infinite
64 recursion by calling D::C::Compare which in turn calls back to your
65 handler.
66 The name of your plugins does not matter, only that it lives in one of
68 those directories. Of course, giving it a sensible name means that the
69 usual installation mechanisms will put it in the right place, and
70 meaningful names will make it easier to debug your code.
71 For an example, look at the plugin that handles Scalar::Properties
73 objects, which is distributed with Data::Compare.
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76 Provided that the above rules are followed I see no reason for you to
77 not upload your plugin to the CPAN yourself. You will need to make
78 Data::Compare a pre-requisite, so that the CPAN.pm installer does the
79 right thing.
80 Alternatively, if you would prefer me to roll your plugin in with the
82 Data::Compare distribution, I'd be happy to do so provided that the
83 code is clear and well-commented, and that you include tests and
84 documentation.
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87 Data::Compare
88 Data::Compare::Plugins::Scalar::Properties
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92 Copyright (c) 2004 David Cantrell <david@cantrell.org.uk>. All rights
93 reserved. This program is free software; you can redistribute it
94 and/or modify it under the same terms as Perl itself.
95perl v5.30.0 2019-09-19 Data::Compare::Plugins(3)