使用元表模拟继承

继承原理: 如果某个成员子类没有, 那就去父类找, 父类没有在往父类找, 直到没有父类
元表原理: 如果某个成员当前对象没有, 就去metatable的__index上找

把两个结合一下: 如果某个成员子类没有, 就去metatable对象的__index上找, 直到没有metatable或metatable对象的__index为nil

 

 1 function class(clsName, superCls)
 2     local cls = {}
 3     cls.__index = cls
 4     cls.__tostring = function(self)
 5         if nil ~= self.super then
 6             self.super.__tostring(self)
 7         end
 8     end
 9     cls.__clsName = clsName
10 
11     if nil ~= superCls then
12         cls.super = superCls
13         if superCls.__index == superCls then
14             setmetatable(cls, superCls)
15         else
16             setmetatable(cls, { __index = superCls })
17         end
18     else
19         cls.ctor = function() --默认构造函数
20         end
21     end
22 
23     cls.new = function(...)
24         local instance = {}
25         setmetatable(instance, cls)
26         instance:ctor(...)
27         return instance
28     end
29 
30     return cls
31 end

 

先定义一个基类：

local Base = class("Base")

function Base:ctor(num, str)
    assert(self.__clsName ~= "Base", "Abstract class can't instance")
    self.num = num
    self.str = str
end

function Base:TestOverride()
    print(self.__clsName, "Base: TestOverride")
end

function Base:TestSuper()
    print(self.__clsName, "Base: TestSuper")
end

function Base:__tostring()
    print(self.__clsName, "Base: num:", self.num, "str:", self.str)
end

 

测试1：

 1 local A = class("A", Base)
 2 function A:TestOverride()
 3     print(self.__clsName, "A: TestOverride")
 4 end
 5 
 6 function A:TestSuper()
 7     self.super.TestSuper(self)
 8     print(self.__clsName, "A: TestSuper")
 9 end
10 
11 function Test1()
12     local a = A.new(5, "A")
13     print("-----")
14     a:TestOverride()
15     print("-----")
16     a:TestSuper()
17     print("-----")
18     tostring(a)
19 end
20 Test1()

运行结果：

A A: TestOverride
-----
A Base: TestSuper
A A: TestSuper
-----
A Base: num: 5 str: A

 

测试2：

 1 local B = class("B", Base)
 2 function B:__tostring()
 3     print(self.__clsName, "B: num:", self.num, "str:", self.str)
 4 end
 5 
 6 
 7 local B_1 = class("B_1", B)
 8 function B_1:TestOverride()
 9     print(self.__clsName, "B_1: TestOverride")
10 end
11 
12 function B_1:TestSuper()
13     self.super.TestSuper(self)
14     print(self.__clsName, "B_1: TestSuper")
15 end
16 
17 
18 local B_2 = class("B_2", B)
19 function B_2:TestOverride()
20     print(self.__clsName, "B_2: TestOverride")
21 end
22 
23 function B_2:__tostring()
24     print(self.__clsName, "B_2: num:", self.num, "str:", self.str)
25 end
26 
27 
28 function Test2()
29     local b_1 = B_1.new(3, "B_1")
30     print("-----")
31     b_1:TestOverride()
32     print("-----")
33     b_1:TestSuper()
34     tostring(b_1)
35 
36     print("-----")
37 
38     local b_2 = B_2.new(4, "B_2")
39     print("-----")
40     b_2:TestOverride()
41     print("-----")
42     b_2:TestSuper()
43     tostring(b_2)
44 end
45 Test2()

运行结果：

B_1 B_1: TestOverride
-----
B_1 Base: TestSuper
B_1 B_1: TestSuper
-----
B_1 B: num: 3 str: B_1
-----
-----
B_2 B_2: TestOverride
-----
B_2 Base: TestSuper
-----
B_2 B_2: num: 4 str: B_2

 

posted @ 2022-02-25 22:13  yanghui01  阅读(45)  评论(0)  编辑  收藏  举报