Lua模块封装：局部表暴露接口的写法

-- 错误：函数与状态全挂全局，互相踩名
function counterAdd(n)
    counterValue = counterValue + n
end

local counter = {value = 0}
local function add(n)
    counter.value = counter.value + n
end
local function reset()
    counter.value = 0
end
local function value()
    return counter.value
end
return {add = add, reset = reset, value = value}