--- name: "Badger::Hub" section: "3pm" platform: "linux" package: "libbadger-perl" version: "0.16-3" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Badger::Hub" --- # Badger::Hub(3pm) central repository of shared resources ## NAME Badger::Hub - central repository of shared resources ## SYNOPSIS ``` use Badger::Hub; # do the happy badger dance! ``` ## INTRODUCTION This documentation describes the `"Badger::Hub"` object. A hub sits in the middle of a Badger application, providing a central point of access to the various other modules, components and sub-system that an application uses. You generally don't need to worry about the `"Badger::Hub"` if you're just a casual user of the Badger modules. It will primarily be of interest to developers who are building their own badger-powered applications or extensions. At present this module is quite basic. It will be developed further in due course. ## DESCRIPTION A `"Badger::Hub"` object is a central repository of shared resources for a Badger application. The hub sits in the middle of an application and provides access to all the individual components and larger sub-systems that may be required. It automatically loads and instantiates these other modules on demand and caches then for subsequent use. ### Components The Badger::Hub base class currently has two components: ``` filesystem => Badger::Filesystem codecs => Badger::Codecs ``` An `"AUTOLOAD"` method allows you to access any component by name. It will be loaded and instantiated automatically. The `"AUTOLOAD"` method also generates the missing method so that you can avoid the overhead of the `"AUTOLOAD"` method the next time you call it. ``` my $filesystem = $hub->filesystem; ``` You can add your own component to a hub and they will be available in the same way. ``` $hub->components( fuzzbox => 'My::Module::Fuzzbox' ); my $fuzzbox = $hub->fuzzbox; ``` ### Delegates As well as accessing components directly, you can also make use of delegate methods that get forwarded onto a component. For example, the hub `"file()"` method is just a short cut to the `"file()"` method of the `"filesystem"` component (implemented by Badger::Filesystem). ``` $file = $hub->file('/path/to/file'); # the short cut $file = $hub->filesystem->file('/path/to/file'); # the long way ``` You can easily define your own delegate methods. ``` $hub->delegates( warm_fuzz => 'fuzzbox' ); $fuzzed = $hub->warm_fuzz; # the short way $fuzzed = $hub->fuzzbox->warm_fuzz; # the long way. ``` ### Subclassing Badger::Hub You can subclass Badger::Hub to define your own collection of components and delegate methods, as shown in the example below. ``` package My::Hub; use Badger::Class version => 0.01, debug => 0, base => 'Badger::Hub'; our $COMPONENTS = { fuzzbox => 'My::Module::Fuzzbox', flanger => 'My::Module::Flanger', }; our $DELEGATES = { warm_fuzz => 'fuzzbox', dirty_noise => 'fuzzbox', wide_flange => 'flanger', wet_flange => 'flanger', }; ``` ### Circular References are a Good Thing In some cases, sub-systems instantiated by a Badger::Hub will also maintain a reference back to the hub. This allows them to access other sub-systems and components that they require. Note that this behaviour implicitly creates circular references between the hub and its delegates. This is intentional. It ensures that the hub and delegates keep each other alive until the hub is explicitly destroyed and the references are freed. Having the hub stick around for as long as possible is usually a Good Thing. It acts as a singleton providing a central point of access to the resources that your application uses (which is a fancy way of saying it's like a global variable). ``` +-----+ +-----------+ | HUB |----->| COMPONENT | | |<-----| | +-----+ +-----------+ ``` If you manually create a hub for whatever reason (and the cases where you would need to are few and far between) then you are responsible for calling the **destroy()** method when you're done with it. This will manually break the circular references and free up any memory used by the hub and any delegates it is using. If you don't call the **destroy()** method then the hub will remain alive until the end of the program when the memory will be freed as usual. In most cases this is perfectly acceptable. However, you generally don't need to worry about any of this because you wouldn't normally create a hub manually. Instead, you would leave it up to the Badger façade (or *"front-end"*) module to do that behind the scenes. When you create a Badger module it implicitly creates a `"Badger::Hub"` to use. When the Badger object goes out of scope its `"DESTROY"` method automatically calls the hub's destroy method. ``` sub foo { my $badger = Badger->new; my $hub = $badger->hub; # do something # $badger object is freed here, that calls $hub->destroy } ``` Because there is no reference from the hub back to the Badger façade object you don't have to worry about circular references. The Badger object is correctly freed and that ensures the hub gets cleaned up. ``` +--------+ +-----+ +-----------+ | BADGER |----->| HUB |----->| COMPONENT | | | | |<-----| | +--------+ +-----+ +-----------+ ``` If you call `"Badger"` methods as class methods then they are forwarded to a prototype object (effectively a singleton object). That in turn will use a prototype hub object. In this case, both the `"Badger"` and `"Badger::Hub"` objects will exist until the end of the program. This ensures that your class methods all *Do the right* *Thing* without you having to worry about creating a Badger object. ``` # class method creates Badger prototype, which creates Badger::Hub # prototype, which loads, instantiates and caches Badger::Filesystem # which can then fetch the file my $file = Badger->file('/path/to/file'); # later... reuse same Badger, Badger::Hub and Badger::Filesystem my $dir = Badger->dir('/path/to/dir'); ``` ## METHODS ### new() Constructor method used to create a new hub object. ``` $hub = Badger::Hub->new(); ``` ### components() This method can be used to get or set entries in the components table for the hub. Components are other modules that the hub can delegate to. ``` # get components hash ref my $comps = $hub->components; # add new components $hub->components({ fuzzbox => 'My::Module::Fuzzbox', flanger => 'My::Module::Flanger', }); ``` ### component($name) This method returns a single entry from the components table. ``` print $hub->component('fuzzbox'); # My::Module::Fuzzbox ``` ### delegates() This method can be used to get or set entries in the delegates table for the hub. This specifies which hub methods should be delegated to components. ``` # get delegates hash ref my $delegs = $hub->delegates; # add new delegates $hub->delegates({ warm_fuzz => 'fuzzbox', dirty_noise => 'fuzzbox', wide_flange => 'flanger', wet_flange => 'flanger', }); ``` ### delegate($name) This method returns a single entry from the delegates table. ``` print $hub->delegate('warm_fuzz'); # fuzzbox ``` ### destroy() This method can be manually called to destroy the hub and any components that it is using. ## INTERNAL METHODS ### construct($component,\\%params) This method configures and instantiates a component. The first argument is the component name. This is mapped to a module via the **component()** method and the module is loaded. A list of named parameters, or a reference to a hash array of named parameters may follow. A reference to the hub is added to these as the `"hub"` item before forwarding them to the constructor method for the component. The component is then cached for subsequent use. ``` # calling the construct() method like this... $hub->construct( fuzzbox => { volume => 11 } ); # ...results in code equivalent to this: use Your::Module::Fuzzbox; Your::Module::Fuzzbox->new({ volume => 11, hub => $hub }); ``` ### auto\_can($name) This method is installed as an auto\_can handler which is called to resolved undefined methods. If the method called matches the name of a component then it calls **auto\_component()** to generate a method to access the component. If it matches the name of a delegate method then it calls **auto\_delegate()** to generate a delegate method. ### auto\_component($name,$module) This method generates a component method named `$name` which accesses an instance of the `$module` component module. ### auto\_delegate($name,$component) This method generates a delegate method named `$name` which delegates to the `$name` method of the `$component` component. ### config() This method returns a reference to a Badger::Config object representing the configuration for the hub. This is still marked experimental. ## AUTHOR Andy Wardley \ ## COPYRIGHT Copyright (C) 2001-2009 Andy Wardley. All Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.