在Java语言中,提供了发射机制,通过发射机制可以通过字符串构造出这个对象,可以获取对象的所有方法(包括私有方法),可以调用私有方法,可以更改成员变量的值(包括私有的成员变量)。
Ruby也是面向对象的高级语言,当然也提供了反射机制,今天我们讨论通过类名称构造类对象的功能。
我们先看普通的构造:
module ModuleA
#the class name, later we will use it to create the corresponding object
CLASS_NAME_OF_WOOD = "ModuleA::Wood"
CLASS_NAME_OF_WOODDESK = "ModuleA::WoodDesk"
CLASS_NAME_OF_WOODCHAIR = "ModuleA::WoodChair"
class Wood
def initialize
@desc = "I am a primal wood"
end
def say
puts @desc
end
end
class WoodDesk < Wood def initialize @desc = "I am a desk made of wood" end def say_private puts "actually, i have some bug but no public" end public :say private :say_private end class WoodChair < Wood def initialize @desc = "I am a chair made of wood" end def say_private puts "I Want get married with a WoodDesk..." end def smile puts "ha hah hah haha ...." end public :say private :say_private, :smile endend
定义了一个基础类Wood,有两个子类:WoodDesk, WoodChair,子类有分别有一个私有方法 say_private。
我们new出对象来执行:
#the normal initailze
wood = ModuleA::Wood.new
wood.say
desk = ModuleA::WoodDesk.new
desk.say
chair = ModuleA::WoodChair.new
chair.say
#try call the private method
puts "desk respond to say_private? #{desk.respond_to? :say_private}"
desk.say_private if desk.respond_to? :say_private
上面代码,执行public方法say,然后尝试执行private方法 say_private,执行先check是否能够执行,返回结果是不能执行,desk.respond_to? :say_private返回false:
I am a primal wood
I am a desk made of wood
I am a chair made of wood
desk respond to say_private? false
好,现在我们通过反射机制来构造对象,并尝试执行其私有方法。
我们注意到模块的定义中有三个常量,定义的是类名称,
#the class name, later we will use it to create the corresponding object
CLASS_NAME_OF_WOOD = "ModuleA::Wood"
CLASS_NAME_OF_WOODDESK = "ModuleA::WoodDesk"
CLASS_NAME_OF_WOODCHAIR = "ModuleA::WoodChair"
下面会通过这三个变量来理解Module.constants方法。
下面代码片段,基于上面的类定义:
#get all module constants
obj_list = Array.new
tmp_const_sym_list = ModuleA.constants
tmp_const_sym_list.each do | sym |
obj_list << ModuleA.const_get(sym) puts "calss = #{sym.class}, value = #{sym}"end
我们注意到 ModuleA.constants,这个方法是Module模块中的,其作用是返回模块中所有常量的Symbol对象。我们看结果输出:
calss = Symbol, value = CLASS_NAME_OF_WOOD
calss = Symbol, value = CLASS_NAME_OF_WOODDESK
calss = Symbol, value = CLASS_NAME_OF_WOODCHAIR
calss = Symbol, value = Wood
calss = Symbol, value = WoodDesk
calss = Symbol, value = WoodChair
从结果中看到,定义的三个常量和类名称都被返回了。所以注意:Ruby中的常量是包含定义的常量(变量)和类名称,注意他们都是Symbol对象。。
不过我们是需要根据类名称构造类对象,那么那三个常量就是没用的,需要删除。我们通过正则表达式匹配名字,来过滤。上面的代码修改一下:
#get all module constants
sym_list = Array.new
tmp_const_sym_list = ModuleA.constants
tmp_const_sym_list.each do | sym |
puts "calss = #{sym.class}, value = #{sym}"
sym_list << ModuleA.const_get(sym) if /^Wood/w*/ =~ sym.to_send
sym_list << ModuleA.const_get(sym) if /^Wood/w*/ =~ sym.to_s,仅保存以Wood开头的symbol,这样我们就过滤掉了那三个常量。找都类名称之后,开始构造对象:
#create object from symbol
obj_list = Array.new
sym_list.each do | sym |
obj = sym.new
obj_list << obj puts "create the object: #{obj}"endbeginobj_list.each do | wood | wood.sayend
调用Symbol的new方法构造出次对象(sym.new),然后我们调用对象的say方法:
create the object: #
create the object: #
create the object: #
I am a primal wood
I am a desk made of wood
I am a chair made of wood
达到了我们预期的结果。
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原创文章,作者:奋斗,如若转载,请注明出处:https://blog.ytso.com/53144.html