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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 trivally 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 wnat 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 directorys 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;
        
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

    Recently tried fixed to find inner packages and to make it 'just work'
    with PAR but there are still some issues.

    However suggestions (and patches) are 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