委托的模式上一篇偷天换日已经解释,这里只讲解里面的Delegator库的实现.
既然采用ruby,它的库一般来说,用起来会更加funny,更加自然.
如同singleton单例库,你写一个类
class Klass
def method
end
end
想让它成为单例类,只需:
require 'singleton'
class Klass
include Singleton
def method
end
end
如此简单,它自动将构造方法置为隐藏,自动加载多
线程锁调用,哇,还是
线程安全,如果是自己写那得不少代码,而且使用ruby的Module机制,无须继承任何类,毫无副作用...
好了,题外话讲完后,我们来看看Delegator吧.
打开ruby库的delegate.rb文件.
代码行有多少,好家伙,大概330行.除去
注释,实际有效代码有100行吧.
第1步看看使用
接口先:
# SimpleDelegator's implementation serves as a nice example here.
#
# class SimpleDelegator < Delegator
# def initialize(obj)
# super # pass obj to Delegator constructor, required
# @_sd_obj = obj # store obj for future use
# end
#
# def __getobj__
# @_sd_obj # return object we are delegating to, required
# end
#
# def __setobj__(obj)
# @_sd_obj = obj # change delegation object, a feature we're providing
# end
#
# # ...
# end
这就是说只要继承Delegator,然后实现__getobj__与__setobj__方法即可.
这个
使用方法在上一篇偷天换日中即用这个方法.
想想也是,如此的接口也很简洁了.
再看如何实现的:
class Delegator
#
# Pass in the _obj_ to delegate method calls to. All methods supported by
# _obj_ will be delegated to.
#
def initialize(obj)
#拿到所有类的实例方法,去掉几个
#因为Kernel是一个module,它会被所有类包含.可参阅RubyHackGuide进行掌握.
preserved = ::Kernel.public_instance_methods(false)
preserved -= ["to_s","to_a","inspect","==","=~","==="]
for t in self.class.ancestors
preserved |= t.public_instance_methods(false)
preserved |= t.private_instance_methods(false)
preserved |= t.protected_instance_methods(false)
break if t == Delegator
end
preserved << "singleton_method_added"
for method in obj.methods
# 搜集到所有实例方法,
# 以下开始利用eval动态往本代理中添加方法
next if preserved.include? method
begin
# 这里的self是实例本身,不是类,请注意.
# 所以定义的方法都是自身可以用,而不是整个委托类.
# 异常处理的时候使用了一个的技巧,将委托的异常信息给去掉了,更加透明了...(好阴啊,如果是库出问题了连个跟踪的地儿都找不到)
eval <<-EOS
def self.#{method}(*args, &block)
begin
__getobj__.__send__(:#{method}, *args, &block)
rescue Exception
$@.delete_if{|s| /:in `__getobj__'$/ =~ s} #`
$@.delete_if{|s| /^\\(eval\\):/ =~ s}
Kernel::raise
end
end
EOS
rescue SyntaxError
raise NameError, "invalid identifier %s" % method, caller(4)
end
end
end
alias initialize_methods initialize
# 这个method_missing是重新实现是怕被委托的那小子动态添加方法,那'我'(委托类)不能不支持啊,所以添加在这里.
# 那我想问原作者,你上述的实现期不多余了,就只为能再透明点啊...
# Handles the magic of delegation through \_\_getobj\_\_.
def method_missing(m, *args)
target = self.__getobj__
unless target.respond_to?(m)
super(m, *args)
end
target.__send__(m, *args)
end
#
# Checks for a method provided by this the delegate object by fowarding the
# call through \_\_getobj\_\_.
#
def respond_to?(m)
return true if super
return self.__getobj__.respond_to?(m)
end
#
# This method must be overridden by subclasses and should return the object
# method calls are being delegated to.
#
# 你继承了后老实实现它吧.
def __getobj__
raise NotImplementedError, "need to define `__getobj__'"
end
# 这些为了可以使用marshal进行外部类存储.
# 如果不使用它,完全不用理会.
# Serialization support for the object returned by \_\_getobj\_\_.
def marshal_dump
__getobj__
end
# Reinitializes delegation from a serialized object.
def marshal_load(obj)
initialize_methods(obj)
__setobj__(obj)
end
end
所有的
解析在上面的注释里了.
这里需要你的ruby技术相当熟练,掌握ruby元编程技能.因能力有限,欢迎就不同的观点进行探讨.
写在这里后,据松本行弘说forwardable模块更加优秀.有时间可以再
研究下.
最后抱怨一下,ruby库的测试不完善啊,偶尔会出现
一些问题,还需要进行猴子补丁..