Example 1 - using a Badger::Modules object

    use Badger::Modules;
    
    my $modules = Badger::Modules->new( 
        path => ['My::Example','Your::Example'],
    );
    
    # load either My::Example::Foo or Your::Example::Foo
    my $foo_module = $modules->module('foo');
    
    # module() returns the module (class) name that was loaded
    my $foo_object = $foo_module->new;

Example 2 - creating a Badger::Modules subclass

    package My::Project::Modules;
    use base 'Badger::Modules';
    our $PATH = 'My::Project';      # or a list reference
    1;

Example 3 - using the Badger::Modules subclass

    use My::Project::Modules;

    # either by creating an object...
    my $modules = My::Project::Modules->new;
    my $module  = $modules->module('foo')
        || die $modules->reason;
    
    # ...or by calling class methods
    my $module  = My::Project::Modules->module('foo')
        || die $modules->reason;

Example 4 - pre-loading modules (TODO)

    # This doesn't work yet
    use My::Project::Module
        preload => 'foo bar baz';

Example 4 - pre-loading modules and exporting constants (MAYBE)

    # Not sure about this.
    use My::Project::Module
        modules => 'foo bar baz';
    
    my $object = FOO_MODULE->new;

What's the Problem?

    use Your::App::Widget;
    
    sub some_code {
        my $widget = Your::App::Widget->new;
        $widget->do_something;
    }

One of the benefits of object oriented programming is that objects of equivalent types are interchangeable. That means that we should be able to replace the "Your::App::Widget" object with a different implementation as long as it has the same interface in terms of the methods it implements. In strictly typed programming languages this equivalence is enforced rigidly, by requiring that both objects share a common base class, expose the same interface, implement a particular role, or some other mechanism. In loosely typed languages like Perl, we have to rely on duck typing: if it looks like a duck, floats like a duck and quacks like a duck then it is a duck (or is close enough to being a duck for practical purposes).

For example, we might want to use a dummy widget object for test purposes.

    use Your::App::MockObject::Widget;
    
    sub some_code {
        my $widget = Your::App::MockObject::Widget->new;
        $widget->do_something;
    }

Or perhaps use a C implementation of a module on platforms that support it.

    use Your::App::XS::Widget;
    
    sub some_code {
        my $widget = Your::App::XS::Widget->new;
        $widget->do_something;
    }

Or maybe an implementation with additional debugging facilities for use during development, but not in production code.

    use Your::App::Developer::Widget;
    
    sub some_code {
        my $widget = Your::App::Developer::Widget->new;
        $widget->do_something;
    }

By now the problem should be apparent. To use a different implementation of the widget object we have to go and manually change the code. Every occurrence of "Your::App::Widget" in every module of your application must be changed to the new module name. Of course, if you were doing this in real life you would probably end up defining a variable to store the name of the relevant class. Something like this perhaps.

    use Your::App::Widget;
    our $WIDGET_CLASS = 'Your::App::Widget';
    
    sub some_code {
        my $widget = $WIDGET_CLASS->new;
        $widget->do_something;
    }

This works well in simple cases. However, if you've designed your application to be suitably modular (thereby promoting reusability of the individual components and extensibility of the system as a whole) then you may have a whole bunch of different modules to load, all of which need similar variables.

    use Your::App::Widget;
    use Your::App::Doodah;
    use Your::App::Thingy;
    our $WIDGET_CLASS = 'Your::App::Widget';
    our $DOODAH_CLASS = 'Your::App::Doodah';
    our $THINGY_CLASS = 'Your::App::Thingy';

Not only is the repetition of "Your::App" in the above code a red flag for refactoring in itself, but we also have to consider the issue of sharing these variables among the various modules that might need access to them. But before we fall too deep into that rabbit hole, let's jump through the looking glass and see how "Badger::Modules" can be used to tackle the problem.

Using Badger::Modules

    use Badger::Modules;
    
    my $modules = Badger::Modules->new( 
        path => 'Your::App' 
    );

Here we've created a "Badger::Modules" object which loads modules under the "Your::App" namespace. To create a "Your::App::Widget" object we can now write the following code.

    my $wclass = $modules->module('Widget');
    my $widget = $wclass->new;

The module() method maps the argument passed to a full class name ("Your::App::Widget"), loads the module if it hasn't already been loaded and then returns the class name. Of course we could combine this into a single expression:

    my $widget = $modules->module('Widget')->new;

The path configuration option can be specified as a reference to a list of namespaces. The "Badger::Modules" module will try each in turn until it finds a matching module.

    my $modules = Badger::Modules->new( 
        path => ['My::App','Your::App'],
    );

Now when you request the "Widget" module you'll get "My::App::Widget" returned if it exists or "Your::App::Widget" if it doesn't.

If neither is available then an error will be thrown as a Badger::Exception object containing an error message of the format "module not found: Widget". You can set the item configuration option to something other than "module" to change this message. For example, setting the "item" to "plugin" will generate a "plugin not found: Widget" message.

    my $modules = Badger::Modules->new( 
        item => 'plugin',
        path => ['My::App::Plugin','Your::App::Plugin'],
    );

If you would rather have the module() method return "undef" to indicate that a module can't be found then set the "tolerant" configuration option to any true value.

    my $modules = Badger::Modules->new( 
        path     => ['My::App','Your::App'],
        tolerant => 1,
    );

It's then up to you to check the return value and handle the case where it is undefined. The error() method (inherited from the Badger::Base base class) can be used to return an error message for the purposes of friendly error reporting.

    my $module = $modules->module('Widget')
        || die $modules->error;         # module not found: Widget

Any other errors encountered while loading a module will be reported using "croak", regardless of the tolerant option. These usually indicate syntax errors requiring immediate attention and thereby warrant the full backtrace that "croak" provides.

Mapping Names

Name is tried as-is first.

    Your::App + Widget = Your::App::Widget

Then we try camel casing it.

    Your::App + nice_widget = Your::App::NiceWidget

This allows us to specify names in lower case with underscores separating words and have them automatically mapped to the correct CamelCase representation for module names.

Lower case + underscores not only looks nicer (IMHO, YMMV) but can also help to eliminate problems on filesystems like HFS that are case insensitive by default. If you're relying on the difference between say, "CGI" and "cgi" in a module name then you're going to have a world of pain the first time you (or someone else) tries to use that code on a shiny new Mac. And yes, that's me speaking from personal experience :-)

You may think this is a brain-dead stupid thing to do. You may be right. But there are brain-dead stupid filesystems out there that we have to accommodate.

Defining a Badger::Modules Subclass

    package My::App::Plugins;
    use base 'Badger::Modules';
    our $PATH = ['My::App::Plugin', 'Your::App::Plugin'];
    1;

The $PATH package variable can be defined to provide the default search path. The $ITEM, $ITEMS, $NAMES and $TOLERANT package variables (not shown) can also be used to set the default values for the corresponding configuration options.

You can then use your subclass like this:

    use My::App::Plugins;
    my $plugins = My::App::Plugins->new;
    my $plugin  = $plugins->module('example');

This will load either "My::App::Plugin::Example" or "Your::App::Plugin::Example", or throw an error to report that the "example" module can't be loaded.

You can provide additional configuration options when you create your subclass object. Any "path" elements specified will be searched after those defined in the $PATH package variable.

    use My::App::Plugins;
    my $plugins = My::App::Plugins->new(
        path => 'Our::App::Plugins',
    );
    my $plugin  = $plugins->module('example');

This will load "My::App::Plugin::Example", "Your::App::Plugin::Example", "Our::App::Plugin::Example" or throw an error.

Using Badger::Modules as a Singleton

    use My::App::Plugins;
    my $plugin  = My::App::Plugins->module('example');

In this case the module() method fetches a singleton prototype object to use (creating it via a call to new(), if necessary). The same prototype object will be re-used for any subsequent class methods.

path / module_path

    # single path location
    my $modules = Badger::Modules->new(
        path => 'My::Modules',
    );

    # multiple path locations
    my $modules = Badger::Modules->new(
        path => ['My::Modules', 'Your::Modules'],
    );

The "module_path" option is an alias for "path".

    my $modules = Badger::Modules->new(
        module_path => ['My::Modules', 'Your::Modules'],
    );

If the "item" configuration option is specified then the name of the "module_path" option will be changed accordingly.

    # setting item to 'wibble' provides 'wibble_path' as alias to 'path'
    my $modules = Badger::Modules->new(
        item        => 'wibble',
        wibble_path => ['My::Modules', 'Your::Modules'],
    );

An $ITEM package variable defined in a subclass module has the same effect.

    package My::App::Plugins;
    use base 'Badger::Modules';
    our $ITEM = 'plugin';
    1;
    
    package main;
    use My::App::Plugins;
    
    my $plugins = My::App::Plugins->new(
        plugin_path => ['My::Plugin', 'Your::Plugin'],
    );

item

    my $modules = Badger::Modules->new(
        item        => 'wibble',
        wibble_path => ['My::Modules', 'Your::Modules'],
    );

A default value can be provided by a $ITEM package variable in a subclass of "Badger::Modules".

    package My::App::Plugins;
    use base 'Badger::Modules';
    our $ITEM = 'plugin';
    1;

Another effect of setting "item" is that it allows you to specify the "path" option using the item name as a prefix.

    my $modules = Badger::Modules->new(
        item        => 'plugin',
        plugin_path => ['My::App::Plugin', 'Your::App::Plugin'],
    );

This can be useful if you've got several different module loaders in an application and want to avoid confusion between the different "path" configuration options.

items

    my $modules = Badger::Modules->new(
        # highly contrived example
        item  => 'attorney_general',
        items => 'attorneys_general',
    );

A default value can be provided by a $ITEMS package variable in a subclass of "Badger::Modules".

    package My::App::Plugins;
    use base 'Badger::Modules';
    our $ITEM  = 'attorney_general';
    our $ITEMS = 'attorneys_general';
    1;

Note that this isn't used in the base class, but some subclasses rely on it to generate useful error messages.

names

This work well enough for most modules, but some do not capitalise consistently. Modules whose names contain acronyms like "URL" are typically prone to a dose of fail.

    $module = $modules->module('url');      # looks for XXX::Url not XXX::URL

If you specify the name in the correct capitalisation then you'll have no problem.

    $module = $modules->module('URL');

If like me you prefer to use case-insensitive throughout and leave it up to the module loader to worry about the correct capitalisation then the "names" option is your friend. You can use to define any number of simple aliases for the module() method to use.

    $modules = Badger::Modules->new(
        path  => ['My::Plugin', 'Your::Plugin'],
        names => {
            url => 'URL',
            cgi => 'CGI',
            foo => 'iFoo::XS'
        }
    );

Note that the values specified in the "names" hash array are partial module names. They will still be applied to the base paths specified in the "path" option to generate complete candidate module paths.

tolerant

new()

module($name)

[ROUGH DRAFT]

    * name is aliased via names lookup table

    * name is expanded to various possible capitalisations
    
    * each base namespace in path is tried...
    
    * with each name...
    
    * until one is located and loaded, in which case found() is called
      (or failed() if an error occurred while loading the module)
    
    * or we exhaust all possibilities, in which case not_found() is called.

modules()

path()

    my $path = $modules->path;

It can be called with arguments to set a new search path. One or more modules namespaces can be specified as arguments:

    $modules->path('My::App', 'Your::App');

These can also be specified as a reference to an array.

    # either
    $modules->path(['My::App', 'Your::App']);
    
    # or
    @namespaces = ('My::App', 'Your::App');
    $modules->path(\@namespaces);

names()

init_modules($config)

If you subclass the "Badger::Modules" module and define your own init() method then it should call the "init_modules()" to perform the base class initialisation either before, after or in between blocks of your own code.

    package Your::Modules;
    use base 'Badger::Modules';
    
    sub init {
        my ($self, $config) = @_;
        # your code here
        $self->init_modules($config);
        # more of your code here
        return $self;
    }

This has the same effect as calling "$self->SUPER::init($config)" but with less ambiguity in the face of multiple inheritance (usually considered a bad thing to be avoided wherever possible) or in obscure cases where you are monkeying around with the heritage (i.e. base classes) of a module and Perl can't reliably resolve the correct init() method at compile time.

module_names($name)

TODO: More on this. Method should possibly be renamed to expand_names()?

found($name,$module)

Subclasses may redefine this method to perform some other functionality.

not_found($name)

Subclasses may redefine this method to perform some other functionality.

failed($message)