define_methodでデフォルト値のある引数を持つメソッドを定義する

define_method_with_arguments_having_default_value.rb

class Test
  def self.method_missing(name, *args)
    klass = class << self; self end
    klass.class_eval do
      define_method(name) do |a = 1, b = 2|
        puts "a: #{a}, b: #{b}"
      end
    end
    if args.length > 1
      __send__(name, args[0], args[1])
    elsif args.length == 1
      __send__(name, args[0])
    else
      __send__(name)
    end
  end
end

Test.hoge("A", "B")
#  => "a: A, b: B"
Test.hoge("C")
#  => "a: C, b: 2"
Test.hoge
#  => "a: 1, b: 2"