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
Attributes
[R] defaults 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.
[R] name The name of this container. May be nil.
[R] parent 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.

    # File lib/needle/container.rb, line 48
48:     def initialize( parent=nil, name=nil )
49:       @root = nil
50:       @builder = nil
51: 
52:       @name = name
53:       @parent = parent
54:       @service_points = Hash.new
55: 
56:       @defaults = ( parent.nil? ? Hash.new : parent.defaults.dup )
57:     end
Public Instance methods
[]( name, *args )

Alias for get

builder()

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

    # File lib/needle/container.rb, line 87
87:     def builder
88:       @builder ||= self[ :definition_context_factory ].new( self )
89:     end
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 }
     # File lib/needle/container.rb, line 106
106:     def define
107:       yield builder if block_given?
108:       builder
109:     end
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
     # File lib/needle/container.rb, line 119
119:     def define!( &block )
120:       raise ArgumentError, "block expected" unless block
121:       builder.instance_eval( &block )
122:       self
123:     end
descended_from?( container )

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
70:     def descended_from?( container )
71:       return true if self == container
72:       return false unless parent
73:       parent.descended_from? container
74:     end
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.

     # File lib/needle/container.rb, line 289
289:     def find_definition( name )
290:       point = @service_points[ name ]
291:       point = parent.find_definition( name ) if parent unless point
292:       point
293:     end
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".

    # File lib/needle/container.rb, line 79
79:     def fullname
80:       parent_name = ( parent ? parent.fullname : nil )
81:       return @name.to_s unless parent_name
82:       "#{parent_name}.#{@name}"
83:     end
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.

This method is also aliased as []
     # File lib/needle/container.rb, line 304
304:     def get( name, *args )
305:       point = find_definition( name )
306:       raise ServiceNotFound, "#{fullname}.#{name}" unless point
307: 
308:       point.instance( *args )
309:     end
has_key?( name )

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

     # File lib/needle/container.rb, line 315
315:     def has_key?( name )
316:       @service_points.has_key?( name )
317:     end
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 }
     # File lib/needle/container.rb, line 261
261:     def intercept( name )
262:       point = find_definition( name )
263:       raise ServiceNotFound, "#{fullname}.#{name}" unless point
264: 
265:       interceptor = self[ :interceptor_impl_factory ].new
266:       point.interceptor interceptor
267: 
268:       interceptor
269:     end
keys()

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

     # File lib/needle/container.rb, line 328
328:     def keys
329:       @service_points.keys
330:     end
knows_key?( name )

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
321:     def knows_key?( name )
322:       return true if has_key?( name )
323:       return parent.knows_key?( name ) if parent
324:       false
325:     end
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
     # File lib/needle/container.rb, line 378
378:     def method_missing( sym, *args )
379:       if knows_key?( sym )
380:         get( sym, *args )
381:       else
382:         super
383:       end
384:     end
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.

     # File lib/needle/container.rb, line 174
174:     def namespace( name, opts={}, &block )
175:       register( name, opts ) do |c,p|
176:         ns = self[ :namespace_impl_factory ].new( c, name )
177:         block.call ns if block
178:         ns
179:       end
180:     end
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.

     # File lib/needle/container.rb, line 248
248:     def namespace_define( name, opts={}, &block )
249:       raise ArgumentError, "block expected" unless block
250:       namespace( name, opts ) { |ns| ns.define( &block ) }
251:       self[name]
252:     end
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.

This method is also aliased as namespace!
     # File lib/needle/container.rb, line 211
211:     def namespace_define!( name, opts={}, &block )
212:       raise ArgumentError, "block expected" unless block
213:       namespace( name, opts ) { |ns| ns.define!( &block ) }
214:       self[name]
215:     end
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 ) }
     # File lib/needle/container.rb, line 279
279:     def pipeline( name )
280:       point = find_definition( name )
281:       raise ServiceNotFound, "#{fullname}.#{name}" unless point
282: 
283:       point.pipeline
284:     end
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
     # File lib/needle/container.rb, line 136
136:     def register( name, opts={}, &callback )
137:       raise ArgumentError, "expect block" unless callback
138: 
139:       name = name.to_s.intern unless name.is_a?( Symbol )
140:       @service_points[ name ] =
141:         ServicePoint.new( self, name, @defaults.merge( opts ), &callback )
142: 
143:       self
144:     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
     # File lib/needle/container.rb, line 353
353:     def require( file, target_name, registration_method=:register_services )
354:       Kernel.require file
355: 
356:       if target_name.is_a?( Module )
357:         target = target_name
358:       else
359:         target = Object
360:         target_name.to_s.split( /::/ ).each do |element|
361:           target = target.const_get( element )
362:         end
363:       end
364: 
365:       target.__send__( registration_method, self )
366:     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.

     # File lib/needle/container.rb, line 390
390:     def respond_to?( sym )
391:       has_key?( sym ) || super
392:     end
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.

    # File lib/needle/container.rb, line 62
62:     def root
63:       return @root if @root
64:       return self if parent.nil?
65:       @root = parent.root
66:     end
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.

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

     # File lib/needle/container.rb, line 408
408:     def use!( opts )
409:       original = @defaults
410:       @defaults = opts
411: 
412:       if block_given?
413:         begin
414:           yield self
415:         ensure
416:           use! original
417:         end
418:       end
419: 
420:       return original
421:     end