为什么[NSDictionary allKeys]不返回一个集合？ [英] Why doesn’t [NSDictionary allKeys] return a set?

问题描述

有一个原因 NSDictionary 以 NSArray 而不是 ？文档已经声明了数组中键的顺序是未定义的，使用一个集合是合乎逻辑的。

Is there a reason for NSDictionary to return its keys as NSArray instead of NSSet? The documentation already states that the order of the keys in the array is undefined, it would sound logical to use a set.

推荐答案

集合往往在API设计中有些被忽略。它们将被包括在大多数时间，但通常在所有其他标准数据结构之后。除此之外，除了最近的NSFastEnumeration之外，在Objective-C中没有通用收集或序列协议 - 每个收集类都完全独立于所有其他类 - 并且在API之后切换到集合变得非常困难已经写入返回数组。

Sets tend to be somewhat neglected in API design. They'll be included most of the time, but usually long after all the other standard data structures. Add on top of that the fact that besides the very recent NSFastEnumeration, there is no general collection or sequence protocol in Objective-C — every collection class is completely independent of all the others — and it becomes very hard to switch to sets after an API has already been written that returns arrays.

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