Lua 原始表访问
示例
有时，您不想触发元方法，而是真正地写或读给定的键，而没有一些巧妙的功能围绕访问进行包装。为此，lua为您提供了原始表访问方法：
-- first, set up a metatable that allows no read/write access
local meta = {
__index = function(object, index)
-- raise an error
error(string.format("the key '%s' is not present in object '%s'", index, object))
end,
__newindex = function(object, index, value)
-- raise an error, this prevents any write access to the table
error(string.format("you are not allowed to write the object '%s'", object))
end
}
local t = { foo = "bar" }
setmetatable(t, meta)
-- both lines raise an error:
--print(t[1])
--t[1] = 42
-- we can now circumvent this problem by using raw access:
print(rawget(t, 1)) -- prints nil
rawset(t, 1, 42) -- ok
-- since the key 1 is now valid, we can use it in a normal manner:
print(t[1])这样，我们现在可以重写ower前__newindex一种方法，以将值实际写入表中：
meta.__newindex = function(object, index, value)
print(string.format("writing the value '%s' to the object '%s' at the key '%s'",
value, object, index))
rawset(object, index, value)
end