NSEnumerator性能vs for循环在Cocoa [英] NSEnumerator performance vs for loop in Cocoa

问题描述

我知道，如果你有一个循环，修改循环中的项目的计数，使用NSEnumerator在集合是确保你的代码爆炸的最好的方法，但我想了解性能之间的折衷， NSEnumerator类和只是一个旧学校for循环

I know that if you have a loop that modifies the count of the items in the loop, using the NSEnumerator on a set is the best way to make sure your code blows up, however I would like to understand the performance tradeoffs between the NSEnumerator class and just an old school for loop

推荐答案

使用新的 ...）在Objective-C 2.0中的语法通常是最快的迭代集合的方法，因为它可以在堆栈上维护一个缓冲区，并获得批量的项目。

Using the new for (... in ...) syntax in Objective-C 2.0 is generally the fastest way to iterate over a collection because it can maintain a buffer on the stack and get batches of items into it.

使用 NSEnumerator 通常是最慢的方法，因为它经常复制被迭代的集合;对于不可变集合，这可以是便宜的（相当于 -retain ），但对于可变集合，它可以导致创建不可变的副本。

Using NSEnumerator is generally the slowest way because it often copies the collection being iterated; for immutable collections this can be cheap (equivalent to -retain) but for mutable collections it can cause an immutable copy to be created.

做你自己的迭代 - 例如，使用 - [NSArray objectAtIndex：] - 通常会落在中间，因为你不会有潜在的复制

Doing your own iteration — for example, using -[NSArray objectAtIndex:] — will generally fall somewhere in between because while you won't have the potential copying overhead, you also won't be getting batches of objects from the underlying collection.

（PS - 这个问题应该标记为Objective-C，而不是C，因为 NSEnumerator 是一个Cocoa类，新的 for（... in ...）语法特定于Objective-C 。）

(PS - This question should be tagged as Objective-C, not C, since NSEnumerator is a Cocoa class and the new for (... in ...) syntax is specific to Objective-C.)

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