Ruby Delegators

class_delegators.rb

require 'forwardable'

class Foo
  extend Forwardable

  # Note: def_delegators, not def_delegator
  def_delegators :ar, :size, :map
  def ar
    [1, 2, 3]
  end
end

f = Foo.new
f.size # => 3
f.map { |x| x * 2 } # => [2, 4, 6]
# f.each # => NoMethodError

module_delegators.rb

require 'forwardable'

module Foo
  extend self
  extend Forwardable
  
  # Note: def_delegators, not def_delegator
  def_delegators :ar, :size, :map
  def ar
    [1, 2, 3]
  end
end

Foo.size # => 3
Foo.map { |x| x * 2 } # => [2, 4, 6]