【高级技巧】读写网关：__index默认值与__newindex白名单的组合

local DEFAULTS = { rate = 100, times = 3, price = 500 }
local ALLOWED = { rate = true, times = true, price = true, owner = true }
local function makeGateway()
    local entity = {}
    return setmetatable({}, {
        __index = function(_, k)
            return entity[k] or DEFAULTS[k]
        end,
        __newindex = function(t, k, v)
            if not ALLOWED[k] then
                error("非法配置字段：" .. tostring(k), 2)
            end
            rawset(entity, k, v)
        end,
    })
end
local cfg = makeGateway()

local function demoGateway(actor)
    actor = getplayerbyname(actor)
    sendmsg(actor, 1, "未配置字段 rate 读到默认值：" .. cfg.rate)
    cfg.times = 5
    sendmsg(actor, 1, "times 已更新为 " .. cfg.times)
    local ok, err = pcall(function() cfg.hakcer = 1 end)
    if not ok then
        sendmsg(actor, 1, "写入被网关拦截：" .. tostring(err))
    end
end