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

- NAME
- SYNOPSIS
- EXAMPLE
- DESCRIPTION
- ADVANCED USAGE
- PLUGIN SEARCHING
- INNER PACKAGES
- OPTIONS
  - sub_name
  - search_path
  - search_dirs
  - instantiate
  - require
  - inner
  - only
  - except
  - package
  - file_regex
  - include_editor_junk
  - follow_symlinks
  - min_depth, max_depth
- TRIGGERS
  - before_require <plugin>
  - on_require_error <plugin> <err>
  - on_instantiate_error <plugin> <err>
  - after_require <plugin>
- METHODs
  - search_path
- BEHAVIOUR UNDER TEST ENVIRONMENT
- @INC hooks and App::FatPacker
- FUTURE PLANS
- DEVELOPMENT
- AUTHOR
- COPYING
- BUGS
- SEE ALSO

# 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.

# 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

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