Class: Needle::Container

Class | Needle::Container
In: | lib/needle/container.rb
Parent: | Object

The container is the heart of Needle‘s model. Every Container instance is a miniature registry, and is really a namespace separate from every other Container instance. Service lookups inside of a container always look in `self` first, and if not found, they then look in their parent container, recursively.

You will rarely need to instantiate a Container directly. Instead, use the Container#namespace method to create new containers.

### Methods

[] builder define define! descended_from? find_definition fullname get has_key? intercept keys knows_key? method_missing namespace namespace! namespace_define namespace_define! new pipeline register require respond_to? root use use!

### Attributes

defaults | [R] | A hash of default options to use when registering services. These defaults also apply to namespaces, so when specifying a new default service model (for instance) there may be unexpected side-effects with the namespaces that are created.
name | [R] | The name of this container. May be `nil`.
parent | [R] | The container that contains this container. This will be `nil` for the root of a hierarchy (see Registry).

### Public Class methods

new( parent=nil, name=nil )

Create a new empty container with the given parent and name. If a parent is given, this container will inherit the defaults of the parent at the time the container was created.

### Public Instance methods

[]( name, *args )

Alias for get

builder()

Returns the DefinitionContext instance that can be used to "build" this container.

define() {|builder if block_given?| ...}

If a block is given, yields the container‘s builder instance to the block. Otherwise, simply returns the builder instance.

Usage:

      container.define do |b|
        b.foo { Bar.new }
        b.baz { Baz.new }
        ...
      end

Or:

      container.define.foo { Bar.new }
      container.define.baz { Baz.new }

define!( &block )

Create a new DefinitionContext around the container, and then evaluate the block within the new context instance (via `instance_eval`).

Usage:

      container.define! do
        calc( :model => :prototype ) { Calc.new( operations ) }
      end

descended_from?( container )

Returns `true` if this container either is the given container or is descended from the given container, and `false` otherwise.

find_definition( name )

Searches the current container and its ancestors for the named service. If found, the service point (the definition of that service) is returned, otherwise `nil` is returned.

fullname()

Return the fully qualified name of this container, which is the container‘s name and all parent‘s names up to the root container, catenated together with dot characters, i.e., "one.two.three".

get( name, *args )

Retrieves the named service, if it exists. Ancestors are searched if the service is not defined by the current container (see find_definition). If the named service does not exist, ServiceNotFound is raised.

Note that this returns the instantiated service, not the service point.

Also, if any pipeline element in the instantiation pipeline does not support extra parameters when extra parameters have been given, then an error will be raised.

has_key?( name )

Returns `true` if this container includes a service point with the given name. Returns `false` otherwise.

intercept( name )

Describe a new interceptor to use that will intercept method calls on the named service. This method returns a new Interceptor instance, which can be used directly to configure the behavior of the interceptor.

Usage:

      container.intercept( :calc ).with { |c| c.logging_interceptor }

keys()

Return an array of the names of all service points in this container.

knows_key?( name )

Returns `true` if this container or any ancestor includes a service point with the given name. Returns `false` otherwise.

method_missing( sym, *args )

As a convenience for accessing services, this delegates any message sent to the container (which has no parameters and no block) to Container#[]. Note that this incurs slightly more overhead than simply calling Container#[] directly, so if performance is an issue, you should avoid this approach.

Usage:

      container.register( :add ) { Adder.new }
      p container.add == container[:add] # => true

namespace( name, opts={}, &block )

Create a new namespace within the container, with the given name. If a block is provided, it will be invoked when the namespace is created, with the new namespace passed to it.

For the curious, namespaces are simply services that are implemented by Container. The two statements are conceptually identical:

      container.namespace( :calc )
      container.register( :calc ) { |c,p| Needle::Container.new( c, p.name ) }

Note that this means that namespaces may be singletons or prototypes, or have immediate or deferred instantiation, and so forth. (The default of immediate, singleton instantiation is sufficient for 99% of the things you‘ll use namespaces for.)

Usage:

      container.namespace( :operations ) do |op|
        op.register( :add ) { Adder.new }
        ...
      end

      adder = container.calc.operations.add

Note: the block is not invoked until the namespace is created, which is not until it is first referenced. If you need the namespace to be created immediately, either use namespace_define or reference the namespace as soon as you‘ve created it.

namespace!( name, opts={}, &block )

Alias for namespace_define!

namespace_define( name, opts={}, &block )

Create a new namespace within the container, with the given name. The block (which is required) will be passed to Container#define on the new namespace.

For the curious, namespaces are simply services that are implemented by Container. The two statements are really identical:

      container.namespace( :calc )
      container.register( :calc ) { |c,p| Needle::Container.new( c, p.name ) }

Note that this means that namespaces may be singletons or prototypes, or have immediate or deferred instantiation, and so forth. (The default of immediate, singleton instantiation is sufficient for 99% of the things you‘ll use namespaces for.)

Usage:

      container.namespace_define( :operations ) do |b|
        b.add { Adder.new }
        ...
      end

      adder = container.calc.operations.add

Note: this method will immediately instantiate the new namespace, unlike namespace. If you want instantiation of the namespace to be deferred, either use a deferring service model (like `:singleton_deferred`) or create the namespace via namespace.

namespace_define!( name, opts={}, &block )

Create a new namespace within the container, with the given name. The block (which is required) will be passed to Container#define! on the new namespace.

For the curious, namespaces are simply services that are implemented by Container. The two statements are really identical:

      container.namespace( :calc )
      container.register( :calc ) { |c,p| Needle::Container.new( c, p.name ) }

Note that this means that namespaces may be singletons or prototypes, or have immediate or deferred instantiation, and so forth. (The default of immediate, singleton instantiation is sufficient for 99% of the things you‘ll use namespaces for.)

Usage:

      container.namespace_define!( :operations ) do
        add { Adder.new }
        ...
      end

      adder = container.calc.operations.add

Note: this method will immediately instantiate the new namespace, unlike namespace. If you want instantiation of the namespace to be deferred, either use a deferring service model (like `:singleton_deferred`) or create the namespace via namespace.

pipeline( name )

Returns the pipeline object for the named service, which allows clients to explicitly manipulate the service‘s instantiation pipeline.

Usage:

      container.pipeline( :calc ).
        add( :initialize ).
        add( :custom ) { |me,*args| me.succ.call( *args ) }

register( name, opts={}, &callback )

Register the named service with the container. When the service is requested (with Container#[]), the associated callback will be used to construct it.

This returns the registry that was used to register the service.

Usage:

      container.register( :calc, :model=>:prototype ) do |c|
        Calc.new( c.operations )
      end

require( file, target_name, registration_method=:register_services )

Require the given file, and then invoke the given registration method on the target module. The container will be passed as the sole parameter to the registration method. This allows you to easily decentralize the definition of services.

Usage:

      container.require( "app/services", "App::Services" )

      # in app/services.rb:

      module App
        module Services

          def register_services( container )
            ...
          end
          module_function :register_services

        end
      end

respond_to?( sym )

Returns true if this container responds to the given message, or if it explicitly contains a service with the given name (see has_key?). In this case, has_key? is used instead of knows_key? so that subcontainers may be used as proper hashes by their parents.

root()

Returns the root of the current hierarchy. If the container is the root, returns self, otherwise calls Container#root on its parent. The value is cached for future reference.

use( opts ) {|self| ...}

Specifies a set of default options to use temporarily. The options are merged with the current set of defaults for the container. The original options are returned, and may be restored by invoking use again with the hash that is returned. If a block is given, the registry will be yielded to it and the options automatically restored when the block returns.

use!( opts ) {|self| ...}

Specifies a set of default options to use temporarily. The original options are returned. This differs from use in that it will completely replace the original options, instead of merging the parameters with the originals.

[Validate]