forward.rb

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

  def_delegator :@queue, :push, :mypush
  def_delegator :@queue, :push
end

require 'forwardable'
module MyQueue
  class<<self
    extend Forwardable
    def queue
      @queue ||= []
    end

    def_delegator :@queue, :push, :mypush
    def_delegator :@queue, :push
  end
end
MyQueue.push(123) # => NoMethodError: undefined method `push' for nil:NilClass
MyQueue.queue # => []
MyQueue.push(123) # => [123]

require 'forwardable'
module MyQueue
  class<<self
    extend Forwardable
    def queue
      @queue ||= []
    end

    def_delegator :queue, :push, :mypush
    def_delegator :queue, :push
  end
end
MyQueue.push(123) # => [123]

require 'forwardable'
module MyQueue
  class<<self
    extend SingleForwardable
    def queue
      @queue ||= []
    end

    def_delegator :@queue, :push, :mypush
    def_delegator :@queue, :push
  end
end
MyQueue.push(123) # => NoMethodError: undefined method `push' for MyQueue:Module