Lua的面向對象，封裝，繼承，多態

概述

　　咱們總所周知對象是由屬性和方法組成的，要用lua要描述一個對象，也必然要有這兩個特性，屬性和方法。lua的基本結構是table，因此Lua的類，其實都是table，由於它能夠存儲普通的變量又能夠存儲方法，咱們利用table就能夠描述一個對象的屬性和方法。

對象

其實lua要模擬一個對象，關鍵就在於__index設置元表索引這塊，它主要起到索引失敗後該怎麼辦，若是它指向一張表，那麼__index索引失敗後，它會到這張表中去查找有沒有你指定的函數或成員值，若是有，__index方法被調用時會返回該函數的返回值。

---
--- 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

這樣一個lua的對象就建立完成了。馬克思教育咱們實踐是檢驗真理的惟一標準，因此咱們用lua的寫面向對象的思想寫一個計算器的demo來看下是怎麼實現繼承與多態。

加法

繼承剛纔寫得Class類，就有了x,y值，能夠進行加法運算，以此類推，咱們進行減法，乘法，除法的類編寫

---
--- Generated by EmmyLua(https://github.com/EmmyLua)
--- Created by hwc
--- DateTime: 2019/12/10 10:17
---
require("operation.Operation")
AddClass = {}
--設置元表爲Class
setmetatable(AddClass,Class)
AddClass.__index = AddClass
function AddClass:new(x,y)
    local self = {}
    --調用父類的構造函數
    self = Class:new(x,y)
    setmetatable(self,AddClass)
    return self
end
--重寫父類函數
function AddClass:getResult()
    return self.x + self.y
end

減法

---
--- 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("除數不能爲零")
        return -1
    end
    return self.x / self.y
end

多態

咱們建立一個管理工廠類，管理全部運算。這樣一來咱們若是要在添加一個開根號或者平方運行，只要在添加根號類和修改工廠的代碼，其餘就原封不動

---
--- 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

添加一個Main類運行

 

 總結

　　一個利用面向對象思想的lua簡單計算器就完成了，咱們宰Lua中模擬了類，繼承，和多態的特徵，起到了可複用，可擴展，解耦的特性，爲lua開發web項目帶來了極大的便利