class Hamster::ReadCopyUpdateHash

def delete(key)
  @lock.synchronize {
    original_value = @hash.get(key)
    @hash = @hash.delete(key)
    original_value
  }
end

def eql?(other)
  instance_of?(other.class) && @hash.eql?(other.instance_variable_get(:@hash))
end

def initialize
  @hash = EmptyHash
  @lock = Mutex.new
end

def method_missing(name, *args, &block)
  @hash.send(name, *args, &block)
end

def put(key, value)
  @lock.synchronize {
    original_value = @hash.get(key)
    @hash = @hash.put(key, value)
    original_value
  }
end