forwardable.md

Forwardable and SingleForwardable

Forwardable and SingleForwardable offer methods to forward (or delegate) method calls to a designated object.

Forwardable

Forwardable supports three methods of delegating methods: def_delegator, def_delegators and delegate.

def_delegator

def_delegator delegates single methods:

class User
  extend Forwardable

  def_delegator :@address, :street
  def_delegator :@address, :city, :address_city

  # basically defines:
  #
  # def street
  #   @address.street
  # end
  #
  # def address_city
  #   @address.city
  # end
end

def_delegators

def_delegators delegates several methods (using def_delegator):

class User
  extend Forwardable

  def_delegators :@address, :street, :city

  # is basically the same as:
  #
  # def_delegator :@address, :street
  # def_delegator :@address, :city
end

When using def_delegators, the __send__ and __id__ methods are ignored so they are not overriden.

delegate

delegate delegates methods (using def_delegator):

class User
  extend Forwardable

  delegate :street => :@address
  delegate :city => :@address

  # or:
  delegate [:street, :city] => :@address

  # or:
  delegate street: :@address, city: :@address

  # is the same as:
  #
  # def_delegator :@address, :street
  # def_delegator :@address, :city
end

SingleForwardable

SingleForwardable works like Forwardable but on the object level:

user = User.new
user.extend(SingleForwardable)

user.def_delegator(:@address, :street)
user.def_delegator(:@address, :city)

# or
user.def_delegators(:@address, :street, :city)

# or
user.delegate([:street, :city] => :@address)