NAME Beam::Wire - Lightweight Dependency Injection Container VERSION version 1.013 SYNOPSIS # wire.yml dbh: class: 'DBI' method: connect args: - 'dbi:mysql:dbname' - { PrintError: 1 } # myscript.pl use Beam::Wire; my $wire = Beam::Wire->new( file => 'wire.yml' ); my $dbh = $wire->get( 'dbh' ); $wire->set( 'dbh' => DBI->new( 'dbi:pgsql:dbname' ) ); DESCRIPTION Beam::Wire is a dependency injection (DI) container. A DI (dependency injection) container is a framework/mechanism where dependency creation and instantiation is handled automatically (e.g. creates instances of classes that implement a given dependency interface on request). DI does not require a container, in-fact, DI without a container is possible and simply infers that dependency creation isn't automatically handled for you (i.e. you have to write code to instantiate the dependencies manually). Dependency injection (DI) at it's core is about creating loosely coupled code by separating construction logic from application logic. This is done by pushing the creation of services (dependencies) to the entry point(s) and writing the application logic so that dependencies are provided for its components. The application logic doesn't know or care how it is supplied with its dependencies; it just requires them and therefore receives them. OVERVIEW Beam::Wire loads a configuration file and stores the specified configuration in the config which is used to resolve it's services. This section will give you an overview of how to declare dependencies and services, and shape your configuration file. WHAT IS A DEPENDENCY? A dependency is a declaration of a component requirement. In layman's terms, a dependency is a class attribute (or any value required for class construction) which will likely be used to define services. WHAT IS A SERVICE? A service is a resolvable interface which may be selected and implemented on behalf of a dependent component, or instantiated and returned per request. In layman's terms, a service is a class configuration which can be used independently or as a dependent of other services. HOW ARE SERVICES CONFIGURED? # databases.yml production_db: class: 'DBI' method: connect args: - 'dbi:mysql:master' - { PrintError: 0, RaiseError: 0 } production_cache: class: 'CHI' args: driver: 'DBI' dbh: { $ref: 'production_db' } development_db: class: 'DBI' method: connect args: - 'dbi:mysql:slave' - { PrintError: 1, RaiseError: 1 } development_cache: class: 'CHI' args: driver: 'DBI' dbh: { $ref: 'development_db' } Service Attributes class The class to instantiate. The class will be loaded and the "method" (below) method called. method The class method to call to construct the object. Defaults to "new". If multiple methods are needed to initialize an object, "method" can be an arrayref of hashrefs, like so: my_service: class: My::Service method: - method: new args: foo: bar - method: set_baz args: - Fizz In this example, first we call "My::Service-"new( foo => "bar" );> to get our object, then we call "$obj-"set_baz( "Fizz" );> as a further initialization step. To chain methods together, add "return: chain": my_service: class: My::Service method: - method: new args: foo: bar - method: set_baz return: chain args: - Fizz - method: set_buzz return: chain args: - Bork This example is equivalent to the following code: my $service = My::Service->new( foo => "bar" )->set_baz( "Fizz" ) ->set_buzz( "Bork" ); args The arguments to the "method" method. This can be either an array or a hash, like so: # array dbh: class: DBI method: connect args: - 'dbi:mysql:dbname' # hash cache: class: CHI args: driver: Memory max_size: 16MB Using the array of arguments, you can give arrayrefs or hashrefs: # arrayref of arrayrefs names: class: 'Set::CrossProduct' args: - - [ 'Foo', 'Barkowictz' ] - [ 'Bar', 'Foosmith' ] - [ 'Baz', 'Bazleton' ] # arrayrefs of hashrefs cache: class: CHI args: - driver: Memory max_size: 16MB extends Inherit and override attributes from another service. dbh: class: DBI method: connect args: - 'dbi:mysql:dbname' dbh_dev: extends: 'dbh' args: - 'dbi:mysql:devdb' Hash "args" will be merged seperately, like so: activemq: class: My::ActiveMQ args: host: example.com port: 61312 user: root password: 12345 activemq_dev: extends: 'activemq' args: host: dev.example.com "activemq_dev" will get the "port", "user", and "password" arguments from the base service "activemq". with Compose roles into the service object. app: class: My::App with: My::FeatureRole otherapp: class: My::App with: - My::FeatureRole - My::OtherFeatureRole This lets you break features out into roles, and compose those roles a la carte on the fly. If you have 20 different optional features, it is difficult to create every possible combination of them. So, "with" allows you to pick the features you want. lifecycle Control how your service is created. The default value, "singleton", will cache the resulting service and return it for every call to "get()". The other value, "factory", will create a new instance of the service every time: today: class: DateTime method: today lifecycle: factory args: time_zone: US/Chicago report_yesterday: class: My::Report args: date: { $ref: today, $method: add, $args: [ "days", "-1" ] } report_today: class: My::Report args: date: { $ref: today } "DateTime-"add> modifies the object and returns the newly-modified object (to allow for method chaining.) Without "lifecycle: factory", the "today" service would become yesterday, making it hard to know what "report_today" would report on. An "eager" value will be created as soon as the container is created. If you have an object that registers itself upon instantiation, you can make sure your object is created as soon as possible by doing "lifecycle: eager". on Attach event listeners using Beam::Emitter. emitter: class: My::Emitter on: before_my_event: $ref: listener $sub: on_before_my_event my_event: - $ref: listener $sub: on_my_event - $ref: other_listener $sub: on_my_event listener: class: My::Listener other_listener: class: My::Listener Now, when the "emitter" fires off its events, they are dispatched to the appropriate listeners. In order to work around a bug in YAML.pm, you can also specify event listeners as an array of hashes: emitter: class: My::Emitter on: - before_my_event: $ref: listener $sub: on_before_my_event - my_event: $ref: listener $sub: on_my_event - my_event: $ref: other_listener $sub: on_my_event Config Services A config service allows you to read a config file and use it as a service, giving all or part of it to other objects in your container. To create a config service, use the "config" key. The value is the path to the file to read. By default, YAML, JSON, XML, and Perl files are supported (via Config::Any). # db_config.yml dsn: 'dbi:mysql:dbname' user: 'mysql' pass: '12345' # container.yml db_config: config: db_config.yml You can pass in the entire config to an object using $ref: # container.yml db_config: config: db_config.yml dbobj: class: My::DB args: conf: $ref: db_config If you only need the config file once, you can create an anonymous config object. # container.yml dbobj: class: My::DB args: conf: $config: db_config.yml The config file can be used as all the arguments to the service: # container.yml dbobj: class: My::DB args: $config: db_config.yml In this example, the constructor will be called like: my $dbobj = My::DB->new( dsn => 'dbi:mysql:dbname', user => 'mysql', pass => '12345', ); You can reference individual items in a configuration hash using $path references: # container.yml db_config: config: db_config.yml dbh: class: DBI method: connect args: - $ref: db_config $path: /dsn - $ref: db_config $path: /user - $ref: db_config $path: /pass NOTE: You cannot use $path and anonymous config objects. Inner Containers Beam::Wire objects can hold other Beam::Wire objects! inner: class: Beam::Wire args: config: dbh: class: DBI method: connect args: - 'dbi:mysql:dbname' cache: class: CHI args: driver: Memory max_size: 16MB Inner containers' contents can be reached from outer containers by separating the names with a slash character: my $dbh = $wire->get( 'inner/dbh' ); Inner Files inner: class: Beam::Wire args: file: inner.yml Inner containers can be created by reading files just like the main container. If the "file" attribute is relative, the parent's "dir" attribute will be added: # share/parent.yml inner: class: Beam::Wire args: file: inner.yml # share/inner.yml dbh: class: DBI method: connect args: - 'dbi:sqlite:data.db' # myscript.pl use Beam::Wire; my $container = Beam::Wire->new( file => 'share/parent.yml', ); my $dbh = $container->get( 'inner/dbh' ); If more control is needed, you can set the dir on the parent container. If even more control is needed, you can make a subclass of Beam::Wire. Service/Configuration References chi: class: CHI args: driver: 'DBI' dbh: { $ref: 'dbh' } dbh: class: DBI method: connect args: - { $ref: dsn } - { $ref: usr } - { $ref: pwd } dsn: value: "dbi:SQLite:memory:" usr: value: "admin" pwd: value: "s3cret" The reuse of service and configuration containers as arguments for other services is encouraged so we have provided a means of referencing those objects within your configuration. A reference is an arugment (a service argument) in the form of a hashref with a $ref key whose value is the name of another service. Optionally, this hashref may contain a $path key whose value is a Data::DPath search string which should return the found data structure from within the referenced service. It is also possible to use raw-values as services, this is done by configuring a service using a single key/value pair with a "value" key whose value contains the raw-value you wish to reuse. ATTRIBUTES file The file attribute contains the file path of the file where Beam::Wire container services are configured (typically a YAML file). The file's contents should form a single hashref. The keys will become the service names. dir The dir attribute contains the directory path to use when searching for inner container files. Defaults to the directory which contains the file specified by the file. config The config attribute contains a hashref of service configurations. This data is loaded by Config::Any using the file specified by the file. services A hashref of services. If you have any services already built, add them here. meta_prefix The character that begins a meta-property inside of a service's "args". This includes $ref, $path, $method, and etc... The default value is '$'. The empty string is allowed. METHODS get( name, [ overrides ] ) The get method resolves and returns the service named "name". "overrides" may be a list of name-value pairs. If specified, get() will create an anonymous service that extends the "name" service with the given config overrides: # test.pl use Beam::Wire; my $wire = Beam::Wire->new( config => { foo => { args => { text => 'Hello, World!', }, }, }, ); my $foo = $wire->get( 'foo', args => { text => 'Hello, Chicago!' } ); print $foo; # prints "Hello, Chicago!" This allows you to create factories out of any service, overriding service configuration at run-time. set The set method configures and stores the specified service. get_config Get the config with the given name, searching inner containers if required new Create a new container. EXCEPTIONS If there is an error internal to Beam::Wire, an exception will be thrown. If there is an error with creating a service or calling a method, the exception thrown will be passed- through unaltered. Beam::Wire::Exception The base exception class Beam::Wire::Exception::Constructor An exception creating a Beam::Wire object Beam::Wire::Exception::Service An exception with service information inside Beam::Wire::Exception::NotFound The requested service or configuration was not found. Beam::Wire::Exception::InvalidConfig The configuration is invalid: * Both "value" and "class" or "extends" are defined. These are mutually-exclusive. AUTHORS * Doug Bell * Al Newkirk COPYRIGHT AND LICENSE This software is copyright (c) 2015 by Doug Bell. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.