lua元表学习

 a = {, }
 b= {, }

 vector2 = {}
 function vector2.Add(v1, v2)
     if(v1 == nil or v2 == nil)then
         return nil
     end
     local res = {}
     res[] = v1[] + v2[]
     res[] = v2[] + v2[]
     return res;
 end

 vector2.__add = vector2.Add

 setmetatable(a, vector2)
 setmetatable(b, vector2)

 res = a + b

 print(res[], res[])

元表操作的一般流程

1.定义原始表

2.定义元表

3.定义元方法

4.设置元表

 str1 = {"I", "love", "lua"}

 myStr = {}
 function myStr.ToString(str)
     res = {}
     for i = , #str do
         res[i] = str[i]
     end
     return table.concat(res, " ")
 end

 myStr.__tostring = myStr.ToString

 setmetatable(str1, myStr)

 print(str1)

str2 = {str1 = "我",str2 = "爱", str3 = "撸啊"}
myStr = {}
function myStr.ToString(str)
    res = {}
    for  i,v in pairs(str) do
       res[#res+] = v
    end

    return table.concat(res, " ")
end

myStr.__tostring = myStr.ToString

setmetatable(str2, myStr)

print(str2)

teststr = {s1 = "", s2 = ""}

mytable = {}
function mytable.tips()
    return "不存在"
end

mytable.__index = mytable.tips;

setmetatable(teststr, mytable)

--TEST CODE
print(teststr["s1"])
print(teststr["s3"])        --  输出不存在

 testStr = {a = "aaa", b = "bbb"}

 testStr.c = "ccc"   ---添加字段
 print(testStr["c"]) ---输出ccc

 function AddValue(tab, k, v)
     print( "你尝试访问的字段不存在"..k)
 end

 setmetatable(testStr, {__newindex = AddValue})      --简化的元方法

 testStr.d = "ddd"   ---添加字段
 print(testStr["d"])     --输出nil

myTab = {}
function TestMethod(tab, num1, num2)
    return num1 + num2
end

setmetatable(myTab, {__call = TestMethod})

 a = myTab(, )
print(a)            --输出3