lua元表学习

a = {1, 2}
b= {3, 4}

vector2 = {}
function vector2.Add(v1, v2)
    if(v1 == nil or v2 == nil)then
        return nil
    end
    local res = {}
    res[1] = v1[1] + v2[1]
    res[2] = v2[1] + v2[2]
    return res;
end

vector2.__add = vector2.Add

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

res = a + b

print(res[1], res[2])

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 = 1, #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+1] = v
    end

    return table.concat(res, " ")
end

myStr.__tostring = myStr.ToString

setmetatable(str2, myStr)

print(str2)

 

teststr = {s1 = "123", s2 = "456"}


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(1, 2)
print(a)            --输出3