項目中有個公會對象，數據大部分存在data中，之前都是 u.data.point這樣訪問，太麻煩了。

于是通過設置__index 使之可以直接訪問屬性，u.point。

但是還是不能直接改屬性，u.point = 4，所以再設置了__newindex。

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在設置了setmetatable之后，不能直接給u添加新屬性，因為設置了__newindex，新的屬性將直接加到u.data中的。

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[c-sharp] view plaincopyprint?

Union?=?{??

????data?=?nil,??

????dirty?=?nil,??

}??

---?生成新的對象??

function?Union:new(o)??

????o?=?o?or?{}??

????setmetatable(o,self)??

????self.__index?=?self??

????return?o??

end??

---?初始化Union數據??

function?Union:init(data)??

????self:initTable()??

????self.data?=?data??

????local?meta?=?{}??

????meta.__index?=?function?(table,?key)??

????????if?Union[key]?~=?nil?then??

????????????return?Union[key]??

????????else??

????????????return?self.data[key]??

????????end??

????end??

????meta.__newindex?=?function(table,key,?value)??

????????self.data[key]?=?value??

????end??

????setmetatable(self,?meta)??

end??

function?Union:initTable()??

????if?self.data?==?nil?then??

????????self.data?=?{}??

????end??

????if?self.dirty?==?nil?then??

????????self.dirty?=?{}??

????end??

end??

function?Union:print()??

????print(self.point,?self.data.point)??

end??

function?pt()??

????print(data1.point,?data2.point,?u.point,?u.data.point)??

end??

u?=?Union:new()??

data1?=?{point?=?3}??

data2?=?{point?=?103}??

u:init(data1)??

pt()??

u.point?=?4??

pt()??

u.data?=?data2??

pt()??

u.point?=?104??

pt()??

Union = {data = nil,dirty = nil, } --- 生成新的對象 function Union:new(o)o = o or {}setmetatable(o,self)self.__index = selfreturn o end --- 初始化Union數據 function Union:init(data)self:initTable()self.data = datalocal meta = {}meta.__index = function (table, key)if Union[key] ~= nil thenreturn Union[key]elsereturn self.data[key]endendmeta.__newindex = function(table,key, value)self.data[key] = valueendsetmetatable(self, meta) end function Union:initTable()if self.data == nil thenself.data = {}endif self.dirty == nil thenself.dirty = {}end end function Union:print()print(self.point, self.data.point) end function pt()print(data1.point, data2.point, u.point, u.data.point) end u = Union:new() data1 = {point = 3} data2 = {point = 103} u:init(data1) pt() u.point = 4 pt() u.data = data2 pt() u.point = 104 pt()

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?

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通過修改__index和__newindex會獲得不同的結果。

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1.正確結果

[c-sharp] view plaincopyprint?

function?Union:init(data)??

????self:initTable()??

????self.data?=?data??

????local?meta?=?{}??

????meta.__index?=?function?(table,?key)??

????????if?Union[key]?~=?nil?then??

????????????return?Union[key]??

????????else??

????????????return?self.data[key]??

????????end??

????end??

????meta.__newindex?=?function(table,key,?value)??

????????self.data[key]?=?value??

????end??

????setmetatable(self,?meta)??

end??

function Union:init(data)self:initTable()self.data = datalocal meta = {}meta.__index = function (table, key)if Union[key] ~= nil thenreturn Union[key]elsereturn self.data[key]endendmeta.__newindex = function(table,key, value)self.data[key] = valueendsetmetatable(self, meta) end

3??? 103??? 3??? 3
4??? 103??? 4??? 4
4??? 103??? 103??? 103
4??? 104??? 104??? 104

?

2.錯誤的__newindex

[c-sharp] view plaincopyprint?

function?Union:init(data)??

????self:initTable()??

????self.data?=?data??

????local?meta?=?{}??

????meta.__index?=?function?(table,?key)??

????????if?Union[key]?~=?nil?then??

????????????return?Union[key]??

????????else??

????????????return?self.data[key]??

????????end??

????end??

????meta.__newindex?=?self.data??

????setmetatable(self,?meta)??

end??

function Union:init(data)self:initTable()self.data = datalocal meta = {}meta.__index = function (table, key)if Union[key] ~= nil thenreturn Union[key]elsereturn self.data[key]endendmeta.__newindex = self.datasetmetatable(self, meta) end

3??? 103??? 3??? 3
4??? 103??? 4??? 4
4??? 103??? 103??? 103
104??? 103??? 103??? 103

3.錯誤的__index

[c-sharp] view plaincopyprint?

function?Union:init(data)??

????self:initTable()??

????self.data?=?data??

????local?meta?=?{}??

????meta.__index?=?function?(table,?key)??

????????if?Union[key]?~=?nil?then??

????????????return?Union[key]??

????????else??

????????????return?data[key]??

????????end??

????end??

????meta.__newindex?=?function(table,key,?value)??

????????self.data[key]?=?value??

????end??

????setmetatable(self,?meta)??

end??

function Union:init(data)self:initTable()self.data = datalocal meta = {}meta.__index = function (table, key)if Union[key] ~= nil thenreturn Union[key]elsereturn data[key]endendmeta.__newindex = function(table,key, value)self.data[key] = valueendsetmetatable(self, meta) end

3??? 103??? 3??? 3
4??? 103??? 4??? 4
4??? 103??? 4??? 103
4??? 104??? 4??? 104

?對象A在內部可以修改HP.外部對象只能訪問對象A的HP,不能修改.

這東西其實可以用__index和__newindex來實現.

__index指向對象A,這樣就可以訪問;

__newindex重寫,修改hp的話,就禁止.就可以完成他的需求.

下面給出簡單的代碼:

function cannotModifyHp(object) ????local proxy = {} ????local mt = { ????????__index = object, ????__newindex = function(t,k,v) ????????if k ~= "hp" then ????????object[k] = v ????????end ????end ????} ????setmetatable(proxy,mt) ????return proxy end ?? object = {hp = 10,age = 11} function object.sethp(self,newhp) ????self.hp = newhp end ?? o = cannotModifyHp(object) ?? o.hp = 100 print(o.hp) ?? o:sethp(111) print(o.hp) ?? object:sethp(100) print(o.hp)

function cannotModifyHp(object) ????local proxy = {} ????local mt = { ????????__index = object, ????__newindex = function(t,k,v) ????????if k ~= "hp" then ????????object[k] = v ????????end ????end ????} ????setmetatable(proxy,mt) ????return proxy end object = {hp = 10,age = 11} function object.sethp(self,newhp) ????self.hp = newhp end ?? o = cannotModifyHp(object) ?? o.hp = 100 print(o.hp) ?? o:sethp(111) print(o.hp) ?? object:sethp(100) print(o.hp)

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這里影響程序的不同結果是upvalue導致的。

由于一般程序中有可能動態改data。所以建議用function設置__index和__newindex，尤其注意各個不同函數中self指向的是什么對象

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