使用NSMutableArray vs NSArray的缺点？ [英] Disadvantage of using NSMutableArray vs NSArray?

问题描述

我使用数组来存储从我的iPhone应用程序中的数据库加载的缓存对象，并且想知道：使用NSMutableArray，我应该知道有什么重大缺点吗？

I'm using an array to store cached objects loaded from a database in my iPhone app, and was wondering: are there any significant disadvantages to using NSMutableArray that I should know of?

编辑：我知道NSMutableArray可以修改，但我正在寻找特定的原因（性能，等..）为什么会使用NSArray代替。

edit: I know that NSMutableArray can be modified, but I'm looking for specific reasons (performance, etc..) why one would use NSArray instead. I assume there would be a performance difference, but I have no idea whether it's significant or not.

推荐答案

如果你正在加载从数据库中获取对象，你已经知道了多少对象，你可能会从 NSMutableArray s 获得最佳性能。 arrayWithCapacity：方法，并添加对象，直到完全，所以它分配所有的内存一次，如果可以。

If you're loading objects from a database and you know exactly how many objects you have, you would likely get the best performance from NSMutableArrays arrayWithCapacity: method, and adding objects to it until full, so it allocates all the memory at once if it can.

场景，他们秘密地是同样的事情 - NSArray 和 NSMutableArray 都实现与 CFArray 通过免费桥接（ CFMutableArrayRef 和 CFArrayRef 是typedef的 __ CFArray * ） *

Behind the scenes, they're secretly the same thing - NSArray and NSMutableArray are both implemented with CFArrays via toll free bridging (a CFMutableArrayRef and a CFArrayRef are typedef's of the same thing, __CFArray *) *

NSArray 和 NSMutableArray 应该具有相同的性能/复杂性（访问时间在最坏的情况下为O（lg N），最好为O（1）内存两个对象会使用 - NSArray 有一个固定的限制，而 NSMutableArray 可以使用尽可能多的空间自由。

NSArray and NSMutableArray should have the same performance/complexity (access time being O(lg N) at worst and O(1) at best) and the only difference being how much memory the two objects would use - NSArray has a fixed limit, while NSMutableArray can use up as much space as you have free.

CFArray.h 有更多的细节。

*：正如Catfish_Man指出的，这不是真的了。

*: As Catfish_Man points out below, this isn't true anymore.

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