Lua 原始表访问

2024-04-12 22:07:03 362

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

Lua 原始表访问

示例

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