【高级技巧】快照回滚：多变量事务的还原点

local function makeGuard(actor, keys)
    actor = getplayerbyname(actor)
    local function snap()
        local s = {}
        for _, k in ipairs(keys) do
            s[k] = getplayvar(actor, "HUMAN", k)
        end
        return s
    end
    local function rollback(s)
        for k, v in pairs(s) do
            setplayvar(actor, "HUMAN", k, v, 1)
        end
    end
    return { snap = snap, rollback = rollback }
end

local function composeSafe(actor)
    actor = getplayerbyname(actor)
    local guard = makeGuard(actor, { "ComposeCnt", "LuckyPoint" })
    local snap = guard.snap()
    setplayvar(actor, "HUMAN", "ComposeCnt",
        (tonumber(getplayvar(actor, "HUMAN", "ComposeCnt")) or 0) + 1, 1)
    if not takeitem(actor, "裁决之杖碎片", 3) then
        guard.rollback(snap)
        sendmsg(actor, 1, "材料不足，事务已还原。")
        return
    end
    giveitem(actor, "裁决之杖", 1)
    sendmsg(actor, 1, "合成完成。")
end