--因為只有當讀寫不存在的域時，才會觸發__index和__newindex
classA = {className = "classA",name="classAInst"}
function classA:new(newobject)
    newobject = newobject or {}
    setmetatable(newobject, {__index = self})--當在newobject找不到key對應的value時，就到self(即classA)類中查找
    return newobject
end
function inherit(p)
    local
 
 newclass = {className = "classB",parent = p}
    setmetatable(newclass,{__index=p})--當在newclass中找不到key對應的value時，就到p類中查找 
    function newclass:new(newobject)
        newobject = newobject or {}
        setmetatable(newobject,{__index = newclass})--當在newobject找不到key對應的value時，就到newclass類中查找 
        return
 
 newobject 
    end
    return newclass
end
testA = classA:new()
print("testA ==> ",testA.className)
print("testA ==> ",testA.name)

testB = inherit(classA):new({name = "testB"})
print("testB ==> ",testB.className)
print("testB ==> ",testB.name)

testC = inherit(classA):new()
print("testC ==> 
 
",testC.className)
print("testC ==> ",testC.name)

testD = inherit(testB):new()
print("testD ==> ",testD.className)
print("testD ==> ",testD.name)

testA ==> classA
testA ==> classAInst
testB ==> classB
testB ==> testB
testC ==> classB
testC ==> classAInst
testD ==> classB
testD ==> testB

lua中使用table實現類和繼承