Ruby 的众多优点之一是可以使用您自己的方法扩展现有类.这就是所谓的类重新开放"或猴子补丁(后者的含义不过，可能会有所不同).

One of the numerous niceties of Ruby is the possibility to extend existing classes with your own methods. That's called "class reopening" or monkey-patching (the meaning of the latter can vary, though).

所以，看看这里:

car = {:make => "bmw", :year => "2003"}
# => {:make=>"bmw", :year=>"2003"}
car.to_json
# NoMethodError: undefined method `to_json' for {:make=>"bmw", :year=>"2003"}:Hash
#   from (irb):11
#   from /usr/bin/irb:12:in `<main>'
require 'json'
# => true
car.to_json
# => "{"make":"bmw","year":"2003"}"

如您所见，require json 神奇地将方法 to_json 带入了我们的 Hash.

As you can see, requiring json has magically brought method to_json to our Hash.