# frozen_string_literal: false
# by Keiju ISHITSUKA(keiju@ishitsuka.com)
# original definition by delegator.rb
# Revised by Daniel J. Berger with suggestions from Florian Gross.
# Documentation by James Edward Gray II and Gavin Sinclair
# The Forwardable module provides delegation of specified
# methods to a designated object, using the methods #def_delegator
# For example, say you have a class RecordCollection which
# contains an array <tt>@records</tt>. You could provide the lookup method
# #record_number(), which simply calls #[] on the <tt>@records</tt>
# def_delegator :@records, :[], :record_number
# We can use the lookup method like so:
# r = RecordCollection.new
# r.record_number(0) # => 4
# 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 # re-open RecordCollection class
# def_delegators :@records, :size, :<<, :map
# r = RecordCollection.new
# r.record_number(0) # => 1
# r << 4 # => [1, 2, 3, 4]
# r.map { |x| x * 2 } # => [2, 4, 6, 8]
# You can even extend regular objects with Forwardable.
# my_hash.extend Forwardable # prepare object for delegation
# my_hash.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts()
# You could use Forwardable as an alternative to inheritance, when you don't want
# to inherit all methods from the superclass. For instance, here is how you might
# add a range of +Array+ instance methods to a new class +Queue+:
# @q = [ ] # prepare delegate object
# # setup preferred interface, enq() and deq()...
# def_delegator :@q, :push, :enq
# def_delegator :@q, :shift, :deq
# # support some general Array methods that fit Queues well
# def_delegators :@q, :clear, :first, :push, :shift, :size
# q.enq "Ruby", "Perl", "Python"
# Be advised, RDoc will not detect delegated methods.
# +forwardable.rb+ provides single-method delegation via the def_delegator and
# def_delegators methods. For full-class delegation via DelegateClass, see
require 'forwardable/impl'
require "forwardable/version"
# Takes a hash as its argument. The key is a symbol or an array of
# symbols. These symbols correspond to method names, instance variable
# names, or constant names (see def_delegator). The value is
# the accessor to which the methods will be delegated.
# delegate method => accessor
# delegate [method, method, ...] => accessor
def instance_delegate(hash)
hash.each do |methods, accessor|
unless defined?(methods.each)
def_instance_delegator(accessor, methods)
methods.each {|method| def_instance_delegator(accessor, method)}
# 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
def def_instance_delegators(accessor, *methods)
next if /\A__(?:send|id)__\z/ =~ method
def_instance_delegator(accessor, method)
# Define +method+ as delegator instance method with an optional
# alias name +ali+. Method calls to +ali+ will be delegated to
# +accessor.method+. +accessor+ should be a method name, instance
# variable name, or constant name. Use the full path to the
# constant if providing the constant name.
# Returns the name of the method defined.
# def_delegator :@queue, :push, :mypush
# def_delegator 'MyQueue::CONST', :to_i
# q.push 23 #=> NoMethodError
def def_instance_delegator(accessor, method, ali = method)
gen = Forwardable._delegator_method(self, accessor, method, ali)
# If it's not a class or module, it's an instance
mod = Module === self ? self : singleton_class
ret = mod.module_eval(&gen)
mod.send(:ruby2_keywords, ali) if RUBY_VERSION >= '2.7'
alias delegate instance_delegate
alias def_delegators def_instance_delegators
alias def_delegator def_instance_delegator
def self._delegator_method(obj, accessor, method, ali)
accessor = accessor.to_s unless Symbol === accessor
obj.method_defined?(accessor) || obj.private_method_defined?(accessor) :
obj.respond_to?(accessor, true)
accessor = "#{accessor}()"
method_call = ".__send__(:#{method}, *args, &block)"
if _valid_method?(method)
loc, = caller_locations(2,1)
mesg = "#{Module === obj ? obj : obj.class}\##{ali} at #{loc.path}:#{loc.lineno} forwarding to private method "
method_call = "#{<<-"begin;"}\n#{<<-"end;".chomp}"
unless defined? _.#{method}
::Kernel.warn #{mesg.dump}"\#{_.class}"'##{method}', uplevel: 1
_.#{method}(*args, &block)
_compile_method("#{<<-"begin;"}\n#{<<-"end;"}", __FILE__, __LINE__+1)
def #{ali}(*args, &block)
# SingleForwardable can be used to setup delegation at the object level as well.
# printer.extend SingleForwardable # prepare object for delegation
# printer.def_delegator "STDOUT", "puts" # add delegation for STDOUT.puts()
# Also, SingleForwardable can be used to set up delegation for a Class or Module.
# 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.
# 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.
# delegate method => accessor
# delegate [method, method, ...] => accessor
def single_delegate(hash)
hash.each do |methods, accessor|
unless defined?(methods.each)
def_single_delegator(accessor, methods)
methods.each {|method| def_single_delegator(accessor, method)}
# 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
def def_single_delegators(accessor, *methods)
next if /\A__(?:send|id)__\z/ =~ method
def_single_delegator(accessor, method)
# def_single_delegator(accessor, method, new_name=method)
# 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.
# Returns the name of the method defined.
def def_single_delegator(accessor, method, ali = method)
gen = Forwardable._delegator_method(self, accessor, method, ali)
ret = instance_eval(&gen)
singleton_class.send(:ruby2_keywords, ali) if RUBY_VERSION >= '2.7'
alias delegate single_delegate
alias def_delegators def_single_delegators
alias def_delegator def_single_delegator
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