Ruby的include和extend

在ruby中基本上有三种引入module的方式 
一、在类定义中引入module后，module中的方法成为类的实例方法。 
在类定义中用include引入module。 
例如： 
Ruby代码 
module Base 
def test 
p "This is a instance method!" 
end 
end 

class Car 
include Base 
end 
Car.new.test => "This is a instance method!" 

module Base
def test
p "This is a instance method!"
end
end

class Car
include Base
end
Car.new.test => "This is a instance method!"

二、在类定义中引入module后，module中的方法成为类的类方法。 
在类定义中用extend引入module。 
例如： 
Ruby代码  
module Base 
def test 
p "This is a instance method!" 
end 
end 

class Car 
extend Base 
end 
Car.test => "This is a class method!" 

module Base
def test
p "This is a instance method!" 
end
end

class Car
extend Base
end
Car.test => "This is a class method!"

三、在类定义中引入module后，module中的方法即有成为类的实例方法，又有成为类的类方法。 
这需要在类定义中引入module时，用include。 
例如： 
Ruby代码  
module Base 
def test 
p "This is a instance method!" 
end 
def self.included(base) 
def base.call 
p "This is a class method---call" 
end 
base.extend(ClassMethods) 
end 
module ClassMethods 
def hello 
p "This is a class method----hello" 
end 
end 
end 

class Car 
include Base 
end 

Car.new.test => "This is a instance method!" 
Car.call => "This is a class method---call" 
Car.hello => "This is a class method---hello" 

module Base
def test
p "This is a instance method!"
end
def self.included(base)
def base.call
p "This is a class method---call"
end
base.extend(ClassMethods)
end
module ClassMethods
def hello
p "This is a class method----hello"
end
end
end

class Car
include Base
end

Car.new.test => "This is a instance method!"
Car.call => "This is a class method---call"
Car.hello => "This is a class method---hello"

参考资料： 
1、http://developer.51cto.com/art/200907/132919.htm 
2、http://juixe.com/techknow/index.php/2006/06/15/mixins-in-ruby/