Separate embedded plugin config from parent config
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Config::MVP::Slicer - Extract embedded plugin config from parent config


version 0.302


my $slicer = Config::MVP::Slicer->new({
  config => $parent->config,

# extract a hashref from the parent config without modifying the plugin
my $plugin_config = $slicer->slice($plugin);

# from plugin bundles:
my $plugin_spec = ['Name', 'Package::Name', {default => 'config'}];
# update the hashref

# with object instances:
my $plugger = App::Plugin::Plugger->new({some => 'config'});
# update 'rw' attributes


This can be used to extract embedded configurations for other plugins out of larger (parent) configurations.

A example where this can be useful is plugin bundles (see Config::MVP::Assembler::WithBundles).

A bundle loads other plugins with a default configuration that works most of the time, but sometimes you wish you could customize the configuration for one of those plugins without having to remove the plugin from the bundle and re-specify it separately.

# mvp config file
Other::Plugin.setting = new value

Now you can accept customizations to plugins into your bundle config and separate them out using this module.



This is the main/parent configuration hashref that contains embedded plugin configurations.


This is coderef that determines if a configuration line matches a plugin's name.

It can be customized by passing an alternate subroutine reference to the constructor.

The sub will receive two arguments:

  • The plugin name portion of the configuration line
  • The name of the plugin being worked on (provided to "slice", for instance).

The default returns true if the current plugin name matches the name from the config line regardless of any leading "@Bundle/" prefixes in the plugin name (as this is a common convention for bundles).

Obviously if the "@Bundle/" prefix is specified in the configuration then it is required to be there for the default sub to match (but multiple other "@Bundle/" prefixes will be allowed before it).

# configuration line: "Foo.attr = value"

$slicer->match_name("Foo", "Foo");            # true
$slicer->match_name("Foo", "@Bar/Foo");       # true
$slicer->match_name("Foo", "Bar");            # false

# configuration line: "@Bar/Foo.attr = value"

$slicer->match_name("@Bar/Foo", "Foo");           # false
$slicer->match_name("@Bar/Foo", "@Bar/Foo");      # true
$slicer->match_name("@Bar/Foo", "@Baz/@Bar/Foo"); # true
$slicer->match_name("@Bar/Foo", "@Baz/Foo");      # false

Subclasses can define _build_match_name (which should return a sub) to overwrite the default.


This works like "match_name" except that the configuration line is compared to the plugin's package (class).

The default returns true if the two values are equal and false otherwise.

If you want to match by package rather than name and you expand packages with (for example) a string prefix you may need to set this to something like:

match_package => sub { rewrite_prefix($_[0]) eq $_[1] }

Subclasses can define _build_match_package (which should return a sub) to overwrite the default.


Regular expression that should match at the beginning of a key before the module name and attribute:

# prefix => 'dynamic\.'
# { 'dynamic.Module::Name.attr' => 'value' }

This can be a string or a compiled regular expression (qr//).

The default is no prefix (empty string '').


A regular expression that will capture the package name in $1 and the attribute name in $2.

The default ((.+?)\.(.+?)) separates plugin name from attribute name with a dot:


NOTE: The regexp should not be anchored since "separator_regexp" uses it as the middle piece of a larger regexp (to add "prefix" and the possible array bracket suffix). Also beware of using a regexp that greedily matches the array bracket suffix as that can confuse things as well.



Returns a compiled regular expression (qr//) combining "prefix", "separator", and the possible trailing array specification (\[.*?\]).



Return a hashref of the config arguments for the plugin determined by $plugin.

This is a slice of the "config" attribute appropriate for the plugin passed to the method.

Starting with a config hashref of:

  'APlug:attr1'   => 'value1',
  'APlug:second'  => '2nd',
  'OtherPlug:attr => '0'

Passing a plugin instance of 'APlug' (or an arrayref of ['APlug', 'Full::Package::APlug', {}]) would return:

  'attr1'   => 'value1',
  'second'  => '2nd'


$slicer->merge($plugin, \%opts);

Get the config slice (see "slice"), then attempt to merge it into the plugin.

If $plugin is an arrayref the hashref will be modified. If it is an object it's attributes should be writable ('rw').

This will append to array references if it was specified as an array or if a preexisting value is an arrayref.

Returns the modified $plugin for convenience.

Possible options:

  • slice - A hashref like that returned from "slice". If not present, "slice" will be called.



Used by other methods to normalize the information about a plugin. Returns a list of ($name, $package, \%config).

If $plugin is an arrayref it will simply dereference it. This can be useful for processing the results of plugin bundles.

If $plugin is an instance of a plugin that has a plugin_name method it will construct the list from that method, ref, and the instance itself.


Often configurations come from an ini file and look like this:

option = value

This gets converted to a hashref:

PluginName->new({ option => 'value' });

To embed configuration for other plugins:

bundle_option = value
Bundled::Plugin.option = other value

The simple 'bundle_option' attribute is for @BigBundle, and the bundle can slice out the Bundled::Plugin configuration and merge it in to that plugin's configuration.

Prefixes can be used (see "prefix"). In this example the prefix is set as "plug.".

plug.Bundled::Plugin.attr = value

Due to limitations of this dynamic passing of unknown options (otherwise known as a hack) values that are arrays cannot be declared ahead of time by the bundle. You can help out by specifying that an attribute should be an array:

Baz.quux[0] = part 1
Baz.quux[1] = part 2

This is required because each line will end up in a hashref:

{ "quux[0]" => "part 1", "quxx[1]" => "part 2" }

The subscripts inside the brackets are used for sorting but otherwise ignored. The "slice" method will sort the keys (alphabetically) to produce:

{ quux => ["part 1", "part 2"] }

For simplicity the keys are sorted alphabetically because quux[1.9] and quux[1.10] probably won't sort the way you intended anyway, so just keep things simple:

Plug.attr[0] = part 1
Plug.attr[1] = part 2
Plug.other[09] = part 1
Plug.other[10] = part 2
Plug.alpha[a] = part 1
Plug.alpha[b] = part 2
Plug.alpha[bc] = part 3
Plug.single[] = subscript not required; only used for sorting



You can find documentation for this module with the perldoc command.

perldoc Config::MVP::Slicer


The following websites have more information about this module, and may be of help to you. As always, in addition to those websites please use your favorite search engine to discover more resources.

Bugs / Feature Requests

Please report any bugs or feature requests by email to bug-config-mvp-slicer at, or through the web interface at You will be automatically notified of any progress on the request by the system.

Source Code

git clone


Randy Stauner


This software is copyright (c) 2011 by Randy Stauner.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.