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Module::Pluggable(3)  User Contributed Perl Documentation Module::Pluggable(3)

NAME
       Module::Pluggable - automatically give your module the ability to have
       plugins

SYNOPSIS
       Simple use Module::Pluggable -

	   package MyClass;
	   use Module::Pluggable;

       and then	later ...

	   use MyClass;
	   my $mc = MyClass->new();
	   # returns the names of all plugins installed	under MyClass::Plugin::*
	   my @plugins = $mc->plugins();

EXAMPLE
       Why would you want to do	this? Say you have something that wants	to
       pass an object to a number of different plugins in turn.	For example
       you may want to extract meta-data from every email you get sent and do
       something with it. Plugins make sense here because then you can keep
       adding new meta data parsers and	all the	logic and docs for each	one
       will be self contained and new handlers are easy	to add without
       changing	the core code. For that, you might do something	like ...

	   package Email::Examiner;

	   use strict;
	   use Email::Simple;
	   use Module::Pluggable require => 1;

	   sub handle_email {
	       my $self	 = shift;
	       my $email = shift;

	       foreach my $plugin ($self->plugins) {
		   $plugin->examine($email);
	       }

	       return 1;
	   }

       .. and all the plugins will get a chance	in turn	to look	at it.

       This can	be trivially extended so that plugins could save the email
       somewhere and then no other plugin should try and do that.  Simply have
       it so that the "examine"	method returns 1 if it has saved the email
       somewhere. You might also want to be paranoid and check to see if the
       plugin has an "examine" method.

	       foreach my $plugin ($self->plugins) {
		   next	unless $plugin->can('examine');
		   last	if     $plugin->examine($email);
	       }

       And so on. The sky's the	limit.

DESCRIPTION
       Provides	a simple but, hopefully, extensible way	of having 'plugins'
       for your	module.	Obviously this isn't going to be the be	all and	end
       all of solutions	but it works for me.

       Essentially all it does is export a method into your namespace that
       looks through a search path for .pm files and turn those	into class
       names.

       Optionally it instantiates those	classes	for you.

ADVANCED USAGE
       Alternatively, if you don't want	to use 'plugins' as the	method ...

	   package MyClass;
	   use Module::Pluggable sub_name => 'foo';

       and then	later ...

	   my @plugins = $mc->foo();

       Or if you want to look in another namespace

	   package MyClass;
	   use Module::Pluggable search_path =>	['Acme::MyClass::Plugin', 'MyClass::Extend'];

       or directory

	   use Module::Pluggable search_dirs =>	['mylibs/Foo'];

       Or if you want to instantiate each plugin rather	than just return the
       name

	   package MyClass;
	   use Module::Pluggable instantiate =>	'new';

       and then

	   # whatever is passed	to 'plugins' will be passed
	   # to	'new' for each plugin
	   my @plugins = $mc->plugins(@options);

       alternatively you can just require the module without instantiating it

	   package MyClass;
	   use Module::Pluggable require => 1;

       since requiring automatically searches inner packages, which may	not be
       desirable, you can turn this off

	   package MyClass;
	   use Module::Pluggable require => 1, inner =>	0;

       You can limit the plugins loaded	using the except option, either	as a
       string, array ref or regex

	   package MyClass;
	   use Module::Pluggable except	=> 'MyClass::Plugin::Foo';

       or

	   package MyClass;
	   use Module::Pluggable except	=> ['MyClass::Plugin::Foo', 'MyClass::Plugin::Bar'];

       or

	   package MyClass;
	   use Module::Pluggable except	=> qr/^MyClass::Plugin::(Foo|Bar)$/;

       and similarly for only which will only load plugins which match.

       Remember	you can	use the	module more than once

	   package MyClass;
	   use Module::Pluggable search_path =>	'MyClass::Filters' sub_name => 'filters';
	   use Module::Pluggable search_path =>	'MyClass::Plugins' sub_name => 'plugins';

       and then	later ...

	   my @filters = $self->filters;
	   my @plugins = $self->plugins;

PLUGIN SEARCHING
       Every time you call 'plugins' the whole search path is walked again.
       This allows for dynamically loading plugins even	at run time. However
       this can	get expensive and so if	you don't expect to want to add	new
       plugins at run time you could do

	 package Foo;
	 use strict;
	 use Module::Pluggable sub_name	=> '_plugins';

	 our @PLUGINS;
	 sub plugins { @PLUGINS	||= shift->_plugins }
	 1;

INNER PACKAGES
       If you have, for	example, a file	lib/Something/Plugin/Foo.pm that
       contains	package	definitions for	both "Something::Plugin::Foo" and
       "Something::Plugin::Bar"	then as	long as	you either have	either the
       require or instantiate option set then we'll also find
       "Something::Plugin::Bar". Nifty!

OPTIONS
       You can pass a hash of options when importing this module.

       The options can be ...

   sub_name
       The name	of the subroutine to create in your namespace.

       By default this is 'plugins'

   search_path
       An array	ref of namespaces to look in.

   search_dirs
       An array	ref of directories to look in before @INC.

   instantiate
       Call this method	on the class. In general this will probably be 'new'
       but it can be whatever you want.	Whatever arguments are passed to
       'plugins' will be passed	to the method.

       The default is 'undef' i.e just return the class	name.

   require
       Just require the	class, don't instantiate (overrides 'instantiate');

   inner
       If set to 0 will	not search inner packages.  If set to 1	will override
       "require".

   only
       Takes a string, array ref or regex describing the names of the only
       plugins to return. Whilst this may seem perverse	... well, it is. But
       it also makes sense. Trust me.

   except
       Similar to "only" it takes a description	of plugins to exclude from
       returning. This is slightly less	perverse.

   package
       This is for use by extension modules which build	on
       "Module::Pluggable": passing a "package"	option allows you to place the
       plugin method in	a different package other than your own.

   file_regex
       By default "Module::Pluggable" only looks for .pm files.

       By supplying a new "file_regex" then you	can change this	behaviour e.g

	   file_regex => qr/\.plugin$/

   include_editor_junk
       By default "Module::Pluggable" ignores files that look like they	were
       left behind by editors. Currently this means files ending in ~ (~), the
       extensions .swp or .swo,	or files beginning with	.#.

       Setting "include_editor_junk" changes "Module::Pluggable" so it does
       not ignore any files it finds.

   follow_symlinks
       Whether,	when searching directories, to follow symlinks.

       Defaults	to 1 i.e do follow symlinks.

   min_depth, max_depth
       This will allow you to set what 'depth' of plugin will be allowed.

       So, for example,	"MyClass::Plugin::Foo" will have a depth of 3 and
       "MyClass::Plugin::Foo::Bar" will	have a depth of	4 so to	only get the
       former (i.e "MyClass::Plugin::Foo") do

	       package MyClass;
	       use Module::Pluggable max_depth => 3;

       and to only get the latter (i.e "MyClass::Plugin::Foo::Bar")

	       package MyClass;
	       use Module::Pluggable min_depth => 4;

TRIGGERS
       Various triggers	can also be passed in to the options.

       If any of these triggers	return 0 then the plugin will not be returned.

   before_require <plugin>
       Gets passed the plugin name.

       If 0 is returned	then this plugin will not be required either.

   on_require_error <plugin> <err>
       Gets called when	there's	an error on requiring the plugin.

       Gets passed the plugin name and the error.

       The default on_require_error handler is to "carp" the error and return
       0.

   on_instantiate_error	<plugin> <err>
       Gets called when	there's	an error on instantiating the plugin.

       Gets passed the plugin name and the error.

       The default on_instantiate_error	handler	is to "carp" the error and
       return 0.

   after_require <plugin>
       Gets passed the plugin name.

       If 0 is returned	then this plugin will be required but not returned as
       a plugin.

METHODs
   search_path
       The method "search_path"	is exported into you namespace as well.	 You
       can call	that at	any time to change or replace the search_path.

	   $self->search_path( add => "New::Path" ); # add
	   $self->search_path( new => "New::Path" ); # replace

BEHAVIOUR UNDER	TEST ENVIRONMENT
       In order	to make	testing	reliable we exclude anything not from blib if
       blib.pm is in %INC.

       However if the module being tested used another module that itself used
       "Module::Pluggable" then	the second module would	fail. This was fixed
       by checking to see if the caller	had (^|/)blib/ in their	filename.

       There's an argument that	this is	the wrong behaviour and	that modules
       should explicitly trigger this behaviour	but that particular code has
       been around for 7 years now and I'm reluctant to	change the default
       behaviour.

       You can now (as of version 4.1) force Module::Pluggable to look outside
       blib in a test environment by doing either

	       require Module::Pluggable;
	       $Module::Pluggable::FORCE_SEARCH_ALL_PATHS = 1;
	       import Module::Pluggable;

       or

	       use Module::Pluggable force_search_all_paths => 1;

@INC hooks and App::FatPacker
       If a module's @INC has a	hook and that hook is an object	which has a
       "files()" method	then we	will try and require those files too. See
       "t/26inc_hook.t"	for an example.

       This has	allowed	App::FatPacker (as of version 0.10.0) to provide
       support for Module::Pluggable.

       This should also, theoretically,	allow someone to modify	PAR to do the
       same thing.

Module::Require	recommended
       Up until	version	5.2 Module::Pluggable used a string "eval" to require
       plugins.

       This has	now been changed to optionally use Module::Runtime and it's
       "require_module"	method when available and fall back to using a path
       based "require" when not.

       It's recommended, but not required, that	you install Module::Runtime.

FUTURE PLANS
       This does everything I need and I can't really think of any other
       features	I want to add. Famous last words of course (not	least because
       we're up	to version 5.0 at the time of writing).

       However suggestions (and	patches) are always welcome.

DEVELOPMENT
       The master repo for this	module is at

       https://github.com/simonwistow/Module-Pluggable

AUTHOR
       Simon Wistow <simon@thegestalt.org>

COPYING
       Copyright, 2006 Simon Wistow

       Distributed under the same terms	as Perl	itself.

BUGS
       None known.

SEE ALSO
       File::Spec, File::Find, File::Basename, Class::Factory::Util,
       Module::Pluggable::Ordered

perl v5.24.1			  2015-08-04		  Module::Pluggable(3)

NAME | SYNOPSIS | EXAMPLE | DESCRIPTION | ADVANCED USAGE | PLUGIN SEARCHING | INNER PACKAGES | OPTIONS | TRIGGERS | METHODs | BEHAVIOUR UNDER TEST ENVIRONMENT | @INC hooks and App::FatPacker | Module::Require recommended | FUTURE PLANS | DEVELOPMENT | AUTHOR | COPYING | BUGS | SEE ALSO

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