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Needle::Container

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.

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 ) click to toggle source

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.

# File lib/needle/container.rb, line 48
def initialize( parent=nil, name=nil )
  @root = nil
  @builder = nil

  @name = name
  @parent = parent
  @service_points = Hash.new

  @defaults = ( parent.nil? ? Hash.new : parent.defaults.dup )
end

Public Instance Methods

[]( name, *args ) click to toggle source
Alias for: get
builder() click to toggle source

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

# File lib/needle/container.rb, line 87
def builder
  @builder ||= self[ :definition_context_factory ].new( self )
end
define() click to toggle source

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 }
# File lib/needle/container.rb, line 106
def define
  yield builder if block_given?
  builder
end
define!( &block ) click to toggle source

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
# File lib/needle/container.rb, line 119
def define!( &block )
  raise ArgumentError, "block expected" unless block
  builder.instance_eval( &block )
  self
end
descended_from?( container ) click to toggle source

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

# File lib/needle/container.rb, line 70
def descended_from?( container )
  return true if self == container
  return false unless parent
  parent.descended_from? container
end
find_definition( name ) click to toggle source

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.

# File lib/needle/container.rb, line 289
def find_definition( name )
  point = @service_points[ name ]
  point = parent.find_definition( name ) if parent unless point
  point
end
fullname() click to toggle source

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".

# File lib/needle/container.rb, line 79
def fullname
  parent_name = ( parent ? parent.fullname : nil )
  return @name.to_s unless parent_name
  "#{parent_name}.#{@name}"
end
get( name, *args ) click to toggle source

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.

# File lib/needle/container.rb, line 304
def get( name, *args )
  point = find_definition( name )
  raise ServiceNotFound, "#{fullname}.#{name}" unless point

  point.instance( self, *args )
end
Also aliased as: []
has_key?( name ) click to toggle source

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

# File lib/needle/container.rb, line 315
def has_key?( name )
  @service_points.has_key?( name )
end
intercept( name ) click to toggle source

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 }
# File lib/needle/container.rb, line 261
def intercept( name )
  point = find_definition( name )
  raise ServiceNotFound, "#{fullname}.#{name}" unless point

  interceptor = self[ :interceptor_impl_factory ].new
  point.interceptor interceptor

  interceptor
end
keys() click to toggle source

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

# File lib/needle/container.rb, line 328
def keys
  @service_points.keys
end
knows_key?( name ) click to toggle source

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

# File lib/needle/container.rb, line 321
def knows_key?( name )
  return true if has_key?( name )
  return parent.knows_key?( name ) if parent
  false
end
method_missing( sym, *args ) click to toggle source

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
# File lib/needle/container.rb, line 378
def method_missing( sym, *args )
  if knows_key?( sym )
    get( sym, *args )
  else
    super
  end
end
namespace( name, opts={}, &block ) click to toggle source

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.

# File lib/needle/container.rb, line 174
def namespace( name, opts={}, &block )
  register( name, opts ) do |c,p|
    ns = self[ :namespace_impl_factory ].new( c, name )
    block.call ns if block
    ns
  end
end
namespace!( name, opts={}, &block ) click to toggle source
Alias for: namespace_define!
namespace_define( name, opts={}, &block ) click to toggle source

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.

# File lib/needle/container.rb, line 248
def namespace_define( name, opts={}, &block )
  raise ArgumentError, "block expected" unless block
  namespace( name, opts ) { |ns| ns.define( &block ) }
  self[name]
end
namespace_define!( name, opts={}, &block ) click to toggle source

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.

# File lib/needle/container.rb, line 211
def namespace_define!( name, opts={}, &block )
  raise ArgumentError, "block expected" unless block
  namespace( name, opts ) { |ns| ns.define!( &block ) }
  self[name]
end
Also aliased as: namespace!
pipeline( name ) click to toggle source

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 ) }
# File lib/needle/container.rb, line 279
def pipeline( name )
  point = find_definition( name )
  raise ServiceNotFound, "#{fullname}.#{name}" unless point

  point.pipeline
end
register( name, opts={}, &callback ) click to toggle source

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
# File lib/needle/container.rb, line 136
def register( name, opts={}, &callback )
  raise ArgumentError, "expect block" unless callback

  name = name.to_s.intern unless name.is_a?( Symbol )
  @service_points[ name ] =
    ServicePoint.new( self, name, @defaults.merge( opts ), &callback )

  self
end
require( file, target_name, registration_method=:register_services ) click to toggle source

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
# File lib/needle/container.rb, line 353
def require( file, target_name, registration_method=:register_services )
  Kernel.require file

  if target_name.is_a?( Module )
    target = target_name
  else
    target = Object
    target_name.to_s.split( /::/ ).each do |element|
      target = target.const_get( element )
    end
  end

  target.__send__( registration_method, self )
end
respond_to?( sym ) click to toggle source

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.

# File lib/needle/container.rb, line 390
def respond_to?( sym )
  has_key?( sym ) || super
end
root() click to toggle source

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.

# File lib/needle/container.rb, line 62
def root
  return @root if @root
  return self if parent.nil?
  @root = parent.root
end
use( opts ) click to toggle source

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.

# File lib/needle/container.rb, line 400
def use( opts, &block ) # :yield: self
  use! @defaults.merge( opts ), &block
end
use!( opts ) click to toggle source

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.

# File lib/needle/container.rb, line 408
def use!( opts )
  original = @defaults
  @defaults = opts

  if block_given?
    begin
      yield self
    ensure
      use! original
    end
  end

  return original
end

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