戻り値がnilであることを保証するだけのdefine_method

void.rb

class Object
  def self.void funcname, &func
    define_method(funcname) { |*args| func.call(*args); nil }
  end
end
if __FILE__ == $PROGRAM_NAME
  require "test/unit"
  class SampleClass
    void :homuhomu do |str|
      $str = str
    end
  end
  class TesVoid < Test::Unit::TestCase
    def setup
      ""
    end
    def test_void
      assert_equal nil, SampleClass.new.homuhomu("string")
      assert_equal "string", $str
    end
  end
end