单例方法与类方法 [英] Singleton method vs. class method
问题描述
类方法和单例方法是一样的还是不同的?这是一个例子.
Are class method and singleton method doing the same or different? Here is an example.
class C
def self.classmethod
puts "class method #{self}"
end
end
C.classmethod # class method C
c = C.new
def c.singletonmethod
puts "instance method #{self}"
end
c.singletonmethod # instance method #<C:0x0000000118ed08>
推荐答案
Ruby 中发生的大部分事情都涉及到类和模块,其中包含实例方法的定义
Most of what happens in Ruby involves classes and modules, containing definitions of instance methods
class C
def talk
puts "Hi!"
end
end
c = C.new
c.talk
Output: Hi!
但是正如您之前看到的(甚至比您看到类中的实例方法还要早),您也可以直接在单个对象上定义单例方法:
But as you saw earlier (even earlier than you saw instance methods inside classes), you can also define singleton methods directly on individual objects:
obj = Object.new
def obj.talk
puts "Hi!"
end
obj.talk
#Output: Hi!
当您在给定对象上定义单例方法时,只有该对象可以调用该方法.如您所见,最常见的单例方法是类方法——一种单独添加到 Class 对象的方法:
When you define a singleton method on a given object, only that object can call that method. As you’ve seen, the most common type of singleton method is the class method—a method added to a Class object on an individual basis:
class Car
def self.makes
%w{ Honda Ford Toyota Chevrolet Volvo }
end
end
但是任何对象都可以添加单例方法.在每个对象的基础上定义方法驱动行为的能力是 Ruby 设计的标志之一.
But any object can have singleton methods added to it. The ability to define method- driven behavior on a per-object basis is one of the hallmarks of Ruby’s design.
单例类是匿名的:虽然它们是类对象(类 Class 的实例),但它们会自动出现而无需命名.尽管如此,您可以打开单例类的类定义主体,并像使用常规类一样向其中添加实例方法、类方法和常量.
Singleton classes are anonymous: although they’re class objects (instances of the class Class ), they spring up automatically without being given a name. Nonetheless, you can open the class-definition body of a singleton class and add instance methods, class methods, and constants to it, as you would with a regular class.
注意:
每个对象都有两个类:
■ 实例所属的类
■ 它的单例类
1:Ruby 对象模型和元编程有关的详细信息单例方法 vs. 类方法 ruby
1: The Ruby Object Model and Metaprogramming For detail info about singleton method vs. class method ruby
2:元编程 - 扩展 Ruby 以获得乐趣和利润 - 作者 戴夫·托马斯
2: MetaProgramming - Extending Ruby for Fun and Profit - by Dave Thomas
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