Read-only table
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- Subject: Read-only table
- From: Ervin Hegedüs <airween@...>
- Date: 2020年6月23日 12:09:11 +0200
Hi,
sorry for this question, may be it's so trivial... but I got
stuck... I just try to understand what's the difference between
two methods below, where I'ld like to make a read only table.
x = {a = "AA"}
function readonlytable(table)
return setmetatable({}, {
__index = table,
__newindex = function(table, key, value)
error("Attempt to add a new or modify an exists item to a read-only table")
end,
__metatable = false
});
end
setmetatable(x, {
__index = x,
__newindex = function(x, key, value)
error("Attempt to add a new or modify an exists item to a read-only table")
end,
__metatable = false
});
Now I try:
x.a = "BB"
which is *works* (this isn't expected)
x.b = "bbb"
*doesn't work* (this is expected)
When I do:
x = readonlytable(x)
and then
x.a = "BB"
then I got (the expected) behavior:
lua5.3: ro2.lua:8: Attempt to add a new or modify an exists item to a read-only table
stack traceback:
[C]: in function 'error'
ro2.lua:8: in metamethod '__newindex'
ro2.lua:24: in main chunk
[C]: in ?
So, why does work the function readonlytable() and why doesn't
the "inline" form of same method?
Thanks,
a.