Lua中设置table为只读属性的方法详解（lua中table.insert）越早知道越好

–[[——————————————————————————
-** 设置table只读 出现改写会抛出lua error
— 用法 local cfg_proxy=read_only(cfg) retur cfg_proxy
— 增加了防重置设置read_only的机制
— lua5.3支持 1）table库支持调用元方法，所以table.remove table.insert 也会抛出错误，
— 2）不用定义__ipairs 5.3 ipairs迭代器支持访问元方法__index，pairs迭代器next不支持故需要元方法__pairs
— 低版本lua此函数不能完全按照预期工作
*]]
function read_only(inputTable)
local travelled_tables={}
local function __read_only(tbl)
if not travelled_tables[tbl] then
local tbl_mt=getmetatable(tbl)
if not tbl_mt then
tbl_mt={}
setmetatable(tbl, tbl_mt)
end

local proxy=tbl_mt.__read_only_proxy
if not proxy then
proxy={}
tbl_mt.__read_only_proxy=proxy
local proxy_mt={
__index=tbl,
__newindex=function (t, k, v) error(“error write to a read-only table with key=” .. tostring(k)) end,
__pairs=function (t) return pairs(tbl) end,
— __ipairs=function (t) return ipairs(tbl) end, 5.3版本不需要此方法
__len=function (t) return #tbl end,
__read_only_proxy=proxy
}
setmetatable(proxy, proxy_mt)
end
travelled_tables[tbl]=proxy
for k, v in pairs(tbl) do
if type(v)==”table” then
tbl[k]=__read_only(v)
end
end
end
return travelled_tables[tbl]
end
return __read_only(inputTable)
end

local t0={k=1}
local t2={
fdsf={456}
}
local t1={
a={456, 89},
b={456,ddss=9, t2=t2},
d=45,
e=”string”,
}
t1.c=t1

local t3=read_only(t1)

print(t3.d, t3.c.e, t3.c.c.b.t2.fdsf)
function q1() t3.d=4555 end
function q2() t3.c.d=90 end
function q3() t3.c.c.b.t2.fdsf=90 end
function q4() table.remove(t3.a) end
function q5() t3.b[ddss]=nil end
function q6() t3[f]=89 end
function q7() table.insert(t3.a, 999) end

print(pcall(q1))
print(pcall(q2))
print(pcall(q3))
print(pcall(q4))
print(pcall(q5))
print(pcall(q6))
print(pcall(q7))
print(t3.a[1])
for k,v in pairs(t3) do
print(“===pairs t3:”,k,v)
end
for k,v in pairs(t3.a) do
print(“===pairs t3.a:”,k,v)
end
for k,v in ipairs(t3) do
print(“===ipairs t3:”,k,v)
end
for k,v in ipairs(t3.a) do
print(“===ipair t3.a”,k,v)
end
print(“len t3:”,#t3)
print(“len t3.a:”, #t3.a)

local t4=read_only(t2)

local t5=read_only(t0)
local t6=read_only(t0)

print(t3.b.t2, read_only(t2))
print(t5, t6, t0)

string table: 0x20d4ba0
false input:17: error write to a read-only table with key=d
false input:17: error write to a read-only table with key=d
false input:17: error write to a read-only table with key=fdsf
false input:17: error write to a read-only table with key=2
false input:17: error write to a read-only table with key=nil
false input:17: error write to a read-only table with key=nil
false input:17: error write to a read-only table with key=3===pairs t3: e string===pairs t3: b table: 0x20ccd60===pairs t3: a table: 0x20d4e70===pairs t3: d 45===pairs t3: c table: 0x20ca700===pairs t3.a: 1 456===pairs t3.a: 2 89===ipair t3.a 1 456===ipair t3.a 2 89
len t3: 0
len t3.a: 2
table: 0x20d4870 table: 0x20d4870
table: 0x20d5690 table: 0x20d5690 table: 0x20d1140

__newindex: The indexing assignment table[key]=value. Like the index event, this event happens when table is not a table or when key is not present in table. The metamethod is looked up in table.

Like with indexing, the metamethod for this event can be either a function or a table. If it is a function, it is called with table, key, and value as arguments. If it is a table, Lua does an indexing assignment to this table with the same key and value. (This assignment is regular, not raw, and therefore can trigger another metamethod.)

Whenever there is a __newindex metamethod, Lua does not perform the primitive assignment. (If necessary, the metamethod itself can call rawset to do the assignment.)

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