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  • forwardable.rb

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SingleForwardable can be used to setup delegation at the object level as well.

printer =
printer.extend SingleForwardable        # prepare object for delegation
printer.def_delegator "STDOUT", "puts"  # add delegation for STDOUT.puts()
printer.puts "Howdy!"

Also, SingleForwardable can be used to set up delegation for a Class or Module.

class Implementation
  def self.service
    puts "serviced!"

module Facade
  extend SingleForwardable
  def_delegator :Implementation, :service

Facade.service #=> serviced!

If you want to use both Forwardable and SingleForwardable, you can use methods def_instance_delegator and #def_single_delegator, etc.

Public Instance Methods

def_delegator(accessor, method, ali = method) click to toggle source
def_delegators(accessor, *methods) click to toggle source
def_single_delegator(accessor, method, new_name=method) click to toggle source

Defines a method method which delegates to accessor (i.e. it calls the method of the same name in accessor). If new_name is provided, it is used as the name for the delegate method.

               # File forwardable.rb, line 259
def def_single_delegator(accessor, method, ali = method)
  str = %Q{
    def #{ali}(*args, &block)
        #{accessor}.__send__(:#{method}, *args, &block)
      rescue Exception
        $@.delete_if{|s| %r"#{Regexp.quote(__FILE__)}"o =~ s} unless Forwardable::debug

  instance_eval(str, __FILE__, __LINE__)
Also aliased as: def_delegator
def_single_delegators(accessor, *methods) click to toggle source

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
               # File forwardable.rb, line 245
def def_single_delegators(accessor, *methods)
  for method in methods
    def_single_delegator(accessor, method)
Also aliased as: def_delegators
delegate(hash) click to toggle source
Alias for: single_delegate
delegate method => accessor click to toggle source
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.

               # File forwardable.rb, line 225
def single_delegate(hash)
  hash.each{ |methods, accessor|
    methods = [methods] unless methods.respond_to?(:each)
    methods.each{ |method|
      def_single_delegator(accessor, method)
Also aliased as: delegate

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