概述
我们总所周知对象是由属性和方法组成的，要用lua要描述一个对象，也必然要有这两个特性，属性和方法。lua的基本结构是table，所以Lua的类，其实都是table，因为它可以存储普通的变量又可以存储方法，我们利用table就可以描述一个对象的属性和方法。
对象
其实lua要模拟一个对象，关键就在于__index设置元表索引这块，它主要起到索引失败后该怎么办，如果它指向一张表，那么__index索引失败后，它会到这张表中去查找有没有你指定的函数或成员值，如果有，__index方法被调用时会返回该函数的返回值。
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc --- DateTime: 2019/12/10 10:14 --- Class = {x,y} Class.__index = Class function Class:new(x,y) local self = {} setmetatable(self,Class) self.x = x self.y = y return self end function Class:getResult() return 0 end
这样一个lua的对象就创建完成了。马克思教育我们实践是检验真理的唯一标准，所以我们用lua的写面向对象的思想写一个计算器的demo来看下是怎么实现继承与多态。
加法
继承刚才写得Class类，就有了x,y值，可以进行加法运算，以此类推，我们进行减法，乘法，除法的类编写
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc --- DateTime: 2019/12/10 10:17 --- require("operation.Operation") AddClass = {} --设置元表为Class setmetatable(AddClass,Class) AddClass.__index = AddClass function AddClass:new(x,y) local self = {} --调用父类的构造函数 self = Class:new(x,y) setmetatable(self,AddClass) return self end --重写父类函数 function AddClass:getResult() return self.x + self.y end
减法
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc. --- DateTime: 2019/12/10 10:35 --- require("operation.Operation") SubClass = {} setmetatable(SubClass,Class) SubClass.__index = SubClass function SubClass:new(x,y) local self = {} self = Class:new(x,y) setmetatable(self,SubClass) return self end function SubClass:getResult() return self.x - self.y end
乘法
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc. --- DateTime: 2019/12/10 10:39 --- require("operation.Operation") MulClass = {} setmetatable(MulClass,Class) MulClass.__index = MulClass function MulClass:new(x,y) local self = {} self = Class:new(x,y) setmetatable(self,MulClass) return self end function MulClass:getResult() return self.x * self.y end
除法
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc. --- DateTime: 2019/12/10 10:42 --- require("operation.Operation") DivClass = {} setmetatable(DivClass,Class) DivClass.__index = DivClass function DivClass:new(x,y) local self = {} self = Class:new(x,y) setmetatable(self,DivClass) return self end function DivClass:getResult() if self.y == 0 then print("除数不能为零") return -1 end return self.x / self.y end
多态
我们创建一个管理工厂类，管理所有运算。这样一来我们如果要在添加一个开根号或者平方运行，只要在添加根号类和修改工厂的代码，其他就原封不动
--- --- Generated by EmmyLua(https://github.com/EmmyLua) --- Created by hwc. --- DateTime: 2019/12/10 10:46 --- require("operation.OperationAdd") require("operation.OperationSub") require("operation.OperationMul") require("operation.OperationDiv") FactoryClass = {} FactoryClass.__index = FactoryClass function FactoryClass:new(x,y,z) local self = {} setmetatable(self,FactoryClass) self.x = x self.y = y self.z = z return self end function FactoryClass:result() local myTable = {} if self.z == "+" then myTable = AddClass:new(self.x,self.y) return myTable elseif self.z == "-" then myTable = SubClass:new(self.x,self.y) return myTable elseif self.z == "*" then myTable = MulClass:new(self.x,self.y) return myTable elseif self.z == "/" then myTable = DivClass:new(self.x,self.y) return myTable end end
添加一个Main类运行
总结
一个利用面向对象思想的lua简单计算器就完成了，我们宰Lua中模拟了类，继承，和多态的特征，起到了可复用，可扩展，解耦的特性，为lua开发web项目带来了极大的便利
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