在没有继承的情况下,如何重写类方法并从新方法中调用原始方法?

这有时很难理解,但需要打开“特征类”,它是与特定类对象关联的单例。该类的语法为<&书信电报;自我完成…结束。

class Time
  alias :old_strftime :strftime

  def strftime
    puts "got here"
    old_strftime
  end
end

class Time
  class << self
    alias :old_now :now
    def now
      puts "got here too"
      old_now
    end
  end
end

t = Time.now
puts t.strftime

class Time
  class << self
    alias_method :old_time_now, :now

    def now
      my_now = old_time_now
      # new code
      my_now
    end
  end
end

class << Time
  alias_method :old_time_now, :now

  def now
    my_now = old_time_now
    # new code
    my_now
  end
end

如果您需要为测试目的重写它(这是我通常想要重写Time.now的原因),Ruby mocking/Stubing框架将很容易为您做到这一点。例如,使用RSpec(使用flexmock):

Time.stub!(:now).and_return(Time.mktime(1970,1,1))

class Foo
  def initialize(clock=Time)
    @clock = clock
  end

  def do_something
    time = @clock.now
    # ...
  end
end

我一直在试图找出如何使用模块重写实例方法。

module Mo
  def self.included(base)
    base.instance_eval do
      alias :old_time_now :now
      def now
        my_now = old_time_now
        puts 'overrided now'
        # new code
        my_now
      end
    end
  end
end
Time.send(:include, Mo) unless Time.include?(Mo)

> Time.now
overrided now
=> Mon Aug 02 23:12:31 -0500 2010