Provided by: libconfig-mvp-perl_2.200013-1_all 
NAME
Config::MVP - multivalue-property package-oriented configuration
VERSION
version 2.200013
SYNOPSIS
If you want a useful synopsis, consider this code which actually comes from
Config::MVP::Assembler:
my $assembler = Config::MVP::Assembler->new;
# Maybe you want a starting section:
my $section = $assembler->section_class->new({ name => '_' });
$assembler->sequence->add_section($section);
# We'll add some values, which will go to the starting section:
$assembler->add_value(x => 10);
$assembler->add_value(y => 20);
# Change to a new section...
$assembler->change_section($moniker);
# ...and add values to that section.
$assembler->add_value(x => 100);
$assembler->add_value(y => 200);
This doesn't make sense? Well, read on.
(You can also read the 2009 RJBS Advent Calendar article
<http://advent.rjbs.manxome.org/2009/2009-12-20.html> on Config::MVP!)
DESCRIPTION
MVP is a mechanism for loading configuration (or other information) for libraries. It
doesn't read a file or a database. It's a helper for things that do.
The idea is that you end up with a Config::MVP::Sequence object, and that you can use that
object to fully configure your library or application. The sequence will contain a bunch
of Config::MVP::Section objects, each of which is meant to provide configuration for a
part of your program. Most of these sections will be directly related to a Perl library
that you'll use as a plugin or helper. Each section will have a name, and every name in
the sequence will be unique.
This is a pretty abstract set of behaviors, so we'll provide some more concrete examples
that should help explain how things work.
PERL VERSION
This module should work on any version of perl still receiving updates from the Perl 5
Porters. This means it should work on any version of perl released in the last two to
three years. (That is, if the most recently released version is v5.40, then this module
should work on both v5.40 and v5.38.)
Although it may work on older versions of perl, no guarantee is made that the minimum
required version will not be increased. The version may be increased for any reason, and
there is no promise that patches will be accepted to lower the minimum required perl.
EXAMPLE
Imagine that we've got a program called DeliveryBoy that accepts mail and does stuff with
it. The "stuff" is entirely up to the user's configuration. He can set up plugins that
will be used on the message. He writes a config file that's read by
Config::MVP::Reader::INI, which is a thin wrapper around Config::MVP used to load MVP-
style config from INI files.
Here's the user's configuration:
[Whitelist]
require_pgp = 1
file = whitelist-family
file = whitelist-friends
file = whitelist-work
[SpamFilter]
filterset = standard
max_score = 5
action = bounce
[SpamFilter / SpamFilter_2]
filterset = aggressive
max_score = 5
action = tag
[VerifyPGP]
[Deliver]
dest = Maildir
The user will end up with a sequence with five sections, which we can represent something
like this:
{ name => 'Whitelist',
package => 'DeliveryBoy::Plugin::Whitelist',
payload => {
require_pgp => 1,
files => [ qw(whitelist-family whitelist-friends whitelist-work) ]
},
},
{ name => 'SpamFilter',
package => 'DeliveryBoy::Plugin::SpamFilter',
payload => {
filterset => 'standard',
max_score => 5,
action => 'bounce',
}
},
{ name => 'SpamFilter_2',
package => 'DeliveryBoy::Plugin::SpamFilter',
payload => {
filterset => 'aggressive',
max_score => 5,
action => 'tag',
},
},
{ name => 'VerifyPGP',
package => 'DeliveryBoy::Plugin::VerifyPGP',
payload => { },
},
{ name => 'Deliver',
package => 'DeliveryBoy::Plugin::Deliver',
payload => { dest => 'Maildir' },
},
The INI reader uses Config::MVP::Assembler to build up configuration section by section as
it goes, so that's how we'll talk about what's going on.
Every section of the config file was converted into a section in the MVP sequence. Each
section has a unique name, which defaults to the name of the INI section. Each section is
also associated with a package, which was expanded from the INI section name. The way
that names are expanded can be customized by subclassing the assembler.
Every section also has a payload -- a hashref of settings. Note that every entry in every
payload is a simple scalar except for one. The "files" entry for the Whitelist section is
an arrayref. Also, note that while it appears as "files" in the final output, it was
given as "file" in the input.
Config::MVP provides a mechanism by which packages can define aliases for configuration
names and an indication of what names correspond to "multi-value parameters." (That's
part of the meaning of the name "MVP.") When the MVP assembler is told to start a section
for "Whitelist" it expands the section name, loads the package, and inspects it for
aliases and multivalue parameters. Then if multiple entries for a non-multivalue
parameter are given, an exception can be raised. Multivalue parameters are always pushed
onto arrayrefs and non-multivalue parameters are left as found.
...so what now?
So, once our DeliveryBoy program has loaded its configuration, it needs to initialize its
plugins. It can do something like the following:
my $sequence = $deliveryboy->load_config;
for my $section ($sequence->sections) {
my $plugin = $section->package->new( $section->payload );
$deliveryboy->add_plugin( $section->name, $plugin );
}
That's it! In fact, allowing this very, very block of code to load configuration and
initialize plugins is the goal of Config::MVP.
The one thing not depicted is the notion of a "root section" that you might expect to see
in an INI file. This can be easily handled by starting your assembler off with a pre-
built section where root settings will end up. For more information on this, look at the
docs for the specific components.
WHAT NEXT?
Making Packages work with MVP
Any package can be used as part of an MVP section. Packages can provide some methods to
help MVP work with them. It isn't a problem if they are not defined
mvp_aliases
This method should return a hashref of name remappings. For example, if it returned this
hashref:
{
file => 'files',
path => 'files',
}
Then attempting to set either the "file" or "path" setting for the section would actually
set the "files" setting.
mvp_multivalue_args
This method should return a list of setting names that may have multiple values and that
will always be stored in an arrayref.
The Assembler
Config::MVP::Assembler is a state machine that makes it easy to build up your MVP-style
configuration by firing off a series of events: new section, new setting, etc. You might
want to subclass it to change the class of sequence or section that's used or to change
how section names are expanded into packages.
Sequences and Sections
Config::MVP::Sequence and Config::MVP::Section are the two most important classes in MVP.
They represent the overall configuration and each section of the configuration,
respectively. They're both fairly simple classes, and you probably won't need to subclass
them, but it's easy.
Examples in the World
For examples of Config::MVP in use, you can look at Dist::Zilla or App::Addex.
AUTHOR
Ricardo Signes <cpan@semiotic.systems>
CONTRIBUTORS
• Alexandr Ciornii <alexchorny@gmail.com>
• George Hartzell <hartzell@alerce.com>
• Karen Etheridge <ether@cpan.org>
• Kent Fredric <kentfredric@gmail.com>
• Philippe Bruhat (BooK) <book@cpan.org>
• Ricardo Signes <rjbs@semiotic.systems>
• Sven Kirmess <sven.kirmess@kzone.ch>
COPYRIGHT AND LICENSE
This software is copyright (c) 2022 by Ricardo Signes.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.