如何在方法内部猴子对红宝石类进行修补 [英] How to monkey patch a ruby class inside a method
问题描述
我无法在方法正文中使用猴子补丁类.
I am unable to monkey patch a class inside a method body.
在方法定义中, 我正在尝试通过两种方式使用类:
Within a method definition, I am trying to use a class in two ways:
1]创建一个实例,并在我正在使用的类中使用方法的原始定义
1] Create an instance and use the orignal definition of a method in the class I am using
2]猴子修补(pverride)类中的一个方法,现在使用具有新方法定义的实例.
2] Monkey patch (pverride) a method in the class and now use an instance with the new method definition.
基本上,我会在程序中同时使用上述两个类的实例.
Basically I would be using both of the above instances of a class in my program.
挑战在于初始化过程中将调用我覆盖的方法,因此在创建类的实例之前必须覆盖它.
The challenge is the method I am overriding gets called during initialization so I have to override it before I create the instance of the class.
这是一个小模型:
class A
def initialize
do_something
end
def do something
#implementation
end
end
现在,我想在相同的方法中使用A两次,但是一次要使用do_something的修改版本 这就是我要尝试的方式:
Now , I want to use A in the same method twice , but once by using a modified version of do_something This is how I am trying to do it:
def my_method
orig_instance = A.new
#patch the class
Class A # ERROR: CLASS DEF IN METHOD BODY
class << self
alias_method :old_do_something, :do_something
def self.do_something
# new implementation
end
end
new_instance = A.new
#restore method
class << self
alias_method :do_something,:old_do_something
def self.do_something
# new implementation
end
end
end # end of method
我得到了(错误:方法主体中的类定义),在这里我试图猴子修补类,因为我试图在方法内部更改类.
I get the (ERROR: CLASS DEF IN METHOD BODY) where I try to monkey patch the class, since I am trying to change the class inside of a method.
如何在方法中实现猴子修补类?
How do I achieve monkey patching the class in a method ?
谢谢
推荐答案
您可以使用Module#class_eval
,Module#instance_eval
和其他一些元编程实用程序来代替使用class Clazz; blabla; end
重新打开Clazz
并对其进行猴子修补. /方法可以完成相同的技巧.而且由于这些方法接受的那个块不会创建新的绑定范围,因此在元编程实践中更加方便.
Instead of using class Clazz; blabla; end
to reopen Clazz
and monkey patch it, you can use Module#class_eval
, Module#instance_eval
and some other meta-programming utilities/methods to do the same trick. And because that block accepted by these methods doesn't create new binding scopes, it is more convenient in meta-programming practice.
def my_method
puts ">> creating orig_instance"
orig_instance = A.new
puts ">> dump orig_instance"
orig_instance.do_something
new_do_something = lambda do
puts "Modified A#do_something"
end
# monkey patch class A so that the modified version of do_something get called
# during initialization of new_instance
A.class_eval do
alias_method :old_do_something, :do_something
define_method :do_something, new_do_something
end
puts ">> creating new_instance"
new_instance = A.new
puts ">> dump before do_something gets restored"
new_instance.do_something
orig_instance.do_something
# add singleton method for the special instance
# so that the instance always calls the modified do_something
new_instance_singleton = class << new_instance; self end
new_instance_singleton.send :define_method, :do_something, new_do_something
# restore the modified do_something
# so that orig_instance and all other instances (except new_instance) have the original definition
A.class_eval do
alias_method :do_something, :old_do_something
end
puts ">> dump for final result"
new_instance.do_something
orig_instance.do_something
end
以下是my_method
调用的输出:
>> creating orig_instance
Original A#do_something
>> dump orig_instance
Original A#do_something
>> creating new_instance
Modified A#do_something
>> dump before do_something gets restored
Modified A#do_something
Modified A#do_something
>> dump for final result
Modified A#do_something
Original A#do_something
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