A simple Ruby memoization/cache class

memo.rb

class Memo
  def initialize
    @mutex = Mutex.new
    @values = {}
  end

  def memoize(key = :_default_key)
    raise ArgumentError, "Block is required" unless block_given?

    @mutex.synchronize do
      if @values.key?(key)
        @values[key]
      else
        @values[key] = yield
      end
    end
  end

  def clear(key = nil)
    @mutex.synchronize do
      if key
        @values.delete(key)
      else
        @values.clear
      end
    end
    nil
  end
end