create_method_on_method_missing.rb

class Prout
  def initialize(delegate)
    @delegate = delegate
  end

  def delegate
    @delegate
  end

  def method_missing(sym, *args, &blk)
    if self.delegate.respond_to?(sym)
      puts "Creating method :#{sym} on delegate"

      # define an instance method so that future calls on that method do not rely on method_missing
      self.instance_eval <<-RUBY
        def #{sym}(*args, &blk)
          self.delegate.__send__(:#{sym}, *args, &blk)
        end
      RUBY

      self.__send__(sym, *args, &blk)
    else
      super
    end
  end

  def a(x)
    puts "a: #{x}"
  end
end

class Meuh
  def b(x, y)
    puts "b: #{x}, #{y}"
    yield(x + y) if block_given?
  end
end


meuh = Meuh.new
prout = Prout.new(meuh)

prout.a(1)
# => a: 1

prout.b(2, 3)
# => Creating method :b on delegate
# => b: 2, 3

prout.b(5, 6) do |sum|
  puts "in block: #{sum}"
end
# b: 5, 6
# in block: 11