1Config::MVP(3)        User Contributed Perl Documentation       Config::MVP(3)
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NAME

6       Config::MVP - multivalue-property package-oriented configuration
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VERSION

9       version 2.200013
10

SYNOPSIS

12       If you want a useful synopsis, consider this code which actually comes
13       from Config::MVP::Assembler:
14
15         my $assembler = Config::MVP::Assembler->new;
16
17         # Maybe you want a starting section:
18         my $section = $assembler->section_class->new({ name => '_' });
19         $assembler->sequence->add_section($section);
20
21         # We'll add some values, which will go to the starting section:
22         $assembler->add_value(x => 10);
23         $assembler->add_value(y => 20);
24
25         # Change to a new section...
26         $assembler->change_section($moniker);
27
28         # ...and add values to that section.
29         $assembler->add_value(x => 100);
30         $assembler->add_value(y => 200);
31
32       This doesn't make sense?  Well, read on.
33
34       (You can also read the 2009 RJBS Advent Calendar article
35       <http://advent.rjbs.manxome.org/2009/2009-12-20.html> on Config::MVP!)
36

DESCRIPTION

38       MVP is a mechanism for loading configuration (or other information) for
39       libraries.  It doesn't read a file or a database.  It's a helper for
40       things that do.
41
42       The idea is that you end up with a Config::MVP::Sequence object, and
43       that you can use that object to fully configure your library or
44       application.  The sequence will contain a bunch of Config::MVP::Section
45       objects, each of which is meant to provide configuration for a part of
46       your program.  Most of these sections will be directly related to a
47       Perl library that you'll use as a plugin or helper.  Each section will
48       have a name, and every name in the sequence will be unique.
49
50       This is a pretty abstract set of behaviors, so we'll provide some more
51       concrete examples that should help explain how things work.
52

PERL VERSION

54       This module should work on any version of perl still receiving updates
55       from the Perl 5 Porters.  This means it should work on any version of
56       perl released in the last two to three years.  (That is, if the most
57       recently released version is v5.40, then this module should work on
58       both v5.40 and v5.38.)
59
60       Although it may work on older versions of perl, no guarantee is made
61       that the minimum required version will not be increased.  The version
62       may be increased for any reason, and there is no promise that patches
63       will be accepted to lower the minimum required perl.
64

EXAMPLE

66       Imagine that we've got a program called DeliveryBoy that accepts mail
67       and does stuff with it.  The "stuff" is entirely up to the user's
68       configuration.  He can set up plugins that will be used on the message.
69       He writes a config file that's read by Config::MVP::Reader::INI, which
70       is a thin wrapper around Config::MVP used to load MVP-style config from
71       INI files.
72
73       Here's the user's configuration:
74
75         [Whitelist]
76         require_pgp = 1
77
78         file = whitelist-family
79         file = whitelist-friends
80         file = whitelist-work
81
82         [SpamFilter]
83         filterset = standard
84         max_score = 5
85         action    = bounce
86
87         [SpamFilter / SpamFilter_2]
88         filterset = aggressive
89         max_score = 5
90         action    = tag
91
92         [VerifyPGP]
93
94         [Deliver]
95         dest = Maildir
96
97       The user will end up with a sequence with five sections, which we can
98       represent something like this:
99
100         { name    => 'Whitelist',
101           package => 'DeliveryBoy::Plugin::Whitelist',
102           payload => {
103             require_pgp => 1,
104             files   => [ qw(whitelist-family whitelist-friends whitelist-work) ]
105           },
106         },
107         { name    => 'SpamFilter',
108           package => 'DeliveryBoy::Plugin::SpamFilter',
109           payload => {
110             filterset => 'standard',
111             max_score => 5,
112             action    => 'bounce',
113           }
114         },
115         { name    => 'SpamFilter_2',
116           package => 'DeliveryBoy::Plugin::SpamFilter',
117           payload => {
118             filterset => 'aggressive',
119             max_score => 5,
120             action    => 'tag',
121           },
122         },
123         { name    => 'VerifyPGP',
124           package => 'DeliveryBoy::Plugin::VerifyPGP',
125           payload => { },
126         },
127         { name    => 'Deliver',
128           package => 'DeliveryBoy::Plugin::Deliver',
129           payload => { dest => 'Maildir' },
130         },
131
132       The INI reader uses Config::MVP::Assembler to build up configuration
133       section by section as it goes, so that's how we'll talk about what's
134       going on.
135
136       Every section of the config file was converted into a section in the
137       MVP sequence.  Each section has a unique name, which defaults to the
138       name of the INI section.  Each section is also associated with a
139       package, which was expanded from the INI section name.  The way that
140       names are expanded can be customized by subclassing the assembler.
141
142       Every section also has a payload -- a hashref of settings.  Note that
143       every entry in every payload is a simple scalar except for one.  The
144       "files" entry for the Whitelist section is an arrayref.  Also, note
145       that while it appears as "files" in the final output, it was given as
146       "file" in the input.
147
148       Config::MVP provides a mechanism by which packages can define aliases
149       for configuration names and an indication of what names correspond to
150       "multi-value parameters."  (That's part of the meaning of the name
151       "MVP.")  When the MVP assembler is told to start a section for
152       "Whitelist" it expands the section name, loads the package, and
153       inspects it for aliases and multivalue parameters.  Then if multiple
154       entries for a non-multivalue parameter are given, an exception can be
155       raised.  Multivalue parameters are always pushed onto arrayrefs and
156       non-multivalue parameters are left as found.
157
158   ...so what now?
159       So, once our DeliveryBoy program has loaded its configuration, it needs
160       to initialize its plugins.  It can do something like the following:
161
162         my $sequence = $deliveryboy->load_config;
163
164         for my $section ($sequence->sections) {
165           my $plugin = $section->package->new( $section->payload );
166           $deliveryboy->add_plugin( $section->name, $plugin );
167         }
168
169       That's it!  In fact, allowing this very, very block of code to load
170       configuration and initialize plugins is the goal of Config::MVP.
171
172       The one thing not depicted is the notion of a "root section" that you
173       might expect to see in an INI file.  This can be easily handled by
174       starting your assembler off with a pre-built section where root
175       settings will end up.  For more information on this, look at the docs
176       for the specific components.
177

WHAT NEXT?

179   Making Packages work with MVP
180       Any package can be used as part of an MVP section.  Packages can
181       provide some methods to help MVP work with them.  It isn't a problem if
182       they are not defined
183
184       mvp_aliases
185
186       This method should return a hashref of name remappings.  For example,
187       if it returned this hashref:
188
189         {
190           file => 'files',
191           path => 'files',
192         }
193
194       Then attempting to set either the "file" or "path" setting for the
195       section would actually set the "files" setting.
196
197       mvp_multivalue_args
198
199       This method should return a list of setting names that may have
200       multiple values and that will always be stored in an arrayref.
201
202   The Assembler
203       Config::MVP::Assembler is a state machine that makes it easy to build
204       up your MVP-style configuration by firing off a series of events: new
205       section, new setting, etc.  You might want to subclass it to change the
206       class of sequence or section that's used or to change how section names
207       are expanded into packages.
208
209   Sequences and Sections
210       Config::MVP::Sequence and Config::MVP::Section are the two most
211       important classes in MVP.  They represent the overall configuration and
212       each section of the configuration, respectively.  They're both fairly
213       simple classes, and you probably won't need to subclass them, but it's
214       easy.
215
216   Examples in the World
217       For examples of Config::MVP in use, you can look at Dist::Zilla or
218       App::Addex.
219

AUTHOR

221       Ricardo Signes <cpan@semiotic.systems>
222

CONTRIBUTORS

224       •   Alexandr Ciornii <alexchorny@gmail.com>
225
226       •   George Hartzell <hartzell@alerce.com>
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228       •   Karen Etheridge <ether@cpan.org>
229
230       •   Kent Fredric <kentfredric@gmail.com>
231
232       •   Philippe Bruhat (BooK) <book@cpan.org>
233
234       •   Ricardo Signes <rjbs@semiotic.systems>
235
236       •   Sven Kirmess <sven.kirmess@kzone.ch>
237
239       This software is copyright (c) 2022 by Ricardo Signes.
240
241       This is free software; you can redistribute it and/or modify it under
242       the same terms as the Perl 5 programming language system itself.
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246perl v5.36.0                      2023-01-20                    Config::MVP(3)
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