【Lua实战】观察者模式：属性变更的自动通知链

---观察者模式：属性的发布订阅
local Observer = { subs = {} }

function Observer.watch(attrKey, callback)
    Observer.subs[attrKey] = Observer.subs[attrKey] or {}
    table.insert(Observer.subs[attrKey], callback)
end

function Observer.notify(attrKey, oldValue, newValue)
    local subs = Observer.subs[attrKey]
    if not subs then return end
    for _, fn in ipairs(subs) do
        local ok, err = pcall(fn, oldValue, newValue)
        if not ok then
            Ops.alert('观察者异常: ' .. tostring(err))
        end
    end
end

---属性的变更触发观察链
function Attr.change(actor, key, newValue)
    local oldValue = Attr.get(actor, key)
    Attr.set(actor, key, newValue)
    Observer.notify(key, oldValue, newValue)
end

---面板订阅攻击力的变更
Observer.watch('attack', function(old, new)
    GUI:Text_SetString(PowerPanel.atkLabel,
        '攻击 ' .. new)
end)

---排行订阅战力的变更
Observer.watch('power', function(old, new)
    Rank.submit(Player.id, new)
end)