The Forwardable module provides delegation of specified methods to a designated object, using the methods def_delegator and def_delegators.

For example, say you have a class RecordCollection which contains an array @records. You could provide the lookup method record_number(), which simply calls [] on the @records array, like this:

class RecordCollection
  extend Forwardable
  def_delegator :@records, :[], :record_number
end

Further, if you wish to provide the methods size, <<, and map, all of which delegate to @records, this is how you can do it:

class RecordCollection
  # extend Forwardable, but we did that above
  def_delegators :@records, :size, :<<, :map
end
f = Foo.new
f.printf ...
f.gets
f.content_at(1)

Also see the example at forwardable.rb.

Methods
D
I
Constants
FORWARDABLE_VERSION = "1.1.0"
 
Attributes
[RW] debug
Instance Public methods
def_delegator(accessor, method, ali = method)
Alias for: def_instance_delegator
def_delegators(accessor, *methods)
Alias for: def_instance_delegators
def_instance_delegator(accessor, method, ali = method)

Define method as delegator instance method with an optional alias name ali. Method calls to ali will be delegated to accessor.method.

class MyQueue
  extend Forwardable
  attr_reader :queue
  def initialize
    @queue = []
  end

  def_delegator :@queue, :push, :mypush
end

q = MyQueue.new
q.mypush 42
q.queue    #=> [42]
q.push 23  #=> NoMethodError
Also aliased as: def_delegator

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 197
def def_instance_delegator(accessor, method, ali = method)
  line_no = __LINE__; str = %Q{
    def #{ali}(*args, &block)
      begin
        #{accessor}.__send__(:#{method}, *args, &block)
      rescue Exception
        $@.delete_if{|s| %r"#{Regexp.quote(__FILE__)}"o =~ s} unless Forwardable::debug
        ::Kernel::raise
      end
    end
  }
  # If it's not a class or module, it's an instance
  begin
    module_eval(str, __FILE__, line_no)
  rescue
    instance_eval(str, __FILE__, line_no)
  end

end
def_instance_delegators(accessor, *methods)

Shortcut for defining multiple delegator methods, but with no provision for using a different name. The following two code samples have the same effect:

def_delegators :@records, :size, :<<, :map

def_delegator :@records, :size
def_delegator :@records, :<<
def_delegator :@records, :map
Also aliased as: def_delegators

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 170
def def_instance_delegators(accessor, *methods)
  methods.delete("__send__")
  methods.delete("__id__")
  for method in methods
    def_instance_delegator(accessor, method)
  end
end
delegate(hash)
Alias for: instance_delegate
delegate method => accessor delegate [method, method, ...] => accessor

Takes a hash as its argument. The key is a symbol or an array of symbols. These symbols correspond to method names. The value is the accessor to which the methods will be delegated.

Also aliased as: delegate

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 150
def instance_delegate(hash)
  hash.each{ |methods, accessor|
    methods = [methods] unless methods.respond_to?(:each)
    methods.each{ |method|
      def_instance_delegator(accessor, method)
    }
  }
end