lua如何设置只读全局变量——通过元方法与环境

function SetReadOnlyVariables(tbTarget, tbVariablesInTable)
    local proxy = {}
    local mt = {
        __index = tbTarget,
        __newindex = function(_, k, v)
            if tbVariablesInTable[k] then
                error("attempt to update a read-only table", 2)
            else
                tbTarget[k] = v
            end
        end
    }
    setmetatable(proxy, mt)
    return proxy
end

g_nReadOnly = 100
print(g_nReadOnly)

__G = SetReadOnlyVariables(_G, {g_nReadOnly = true})
setfenv(1, __G)

rawset(getfenv(1), "g_nReadOnly", 200) -- can not set g_nReadOnly = 100 directly
print(g_nReadOnly) -- equivalent to print(__G.g_nReadOnly), is 200
print(_G.g_nReadOnly) -- is 100

注解：

__G = SetReadOnlyVariables(_G, {g_nReadOnly = true})：设置_G table中的g_nReadOnly变量为只读。返回一个空表，通过其元表来访问元素。在__newindex方法中对访问权限进行检查。

setfenv(1, __G)：切换当前函数（栈）环境。