是否有过一个理由返回一个IEnumerable时，不使用“收益回报”？ [英] Is there ever a reason to not use 'yield return' when returning an IEnumerable?

问题描述

简单的例子 - 你有一个方法或返回一个IEnumerable属性，主叫方被遍历，在foreach（）循环。如果你的总是的使用您的IEnumerable的方法收益率回报呢？是否有过一个理由不？虽然我明白，它可能并不总是必要的，甚至是更好（也许是例如一个非常小集合），是有过一个理由来主动避免这样做？

Simple example - you have a method or a property that returns an IEnumerable and the caller is iterating over that in a foreach() loop. Should you always be using 'yield return' in your IEnumerable method? Is there ever a reason not to? While I understand that it may not always be necessary to, or even "better" (maybe it's a very small collection for example), is there ever a reason to actively avoid doing this?

中的代码，让我想到了，这是我写的非常相似，在这个线程接受的答案的函数的位 - 的 http://stackoverflow.com/questions/1847580/how-do-i-loop-through-a-date-range

The bit of code that got me thinking about this was a function I wrote very similar to the accepted answer in this thread - http://stackoverflow.com/questions/1847580/how-do-i-loop-through-a-date-range

推荐答案

迭代器块来执行一个活的评价每次都重复一次。

不过，有时候你想要的行为是结果是一个快照在某个时间点。在这种情况下，你可能不希望使用收益回报率，而是返回一个列表与LT;> 或设置，或其他一些持久化集合来代替。

Sometimes, however, the behavior you want is for the results to be a "snapshot" at a point in time. In these cases you probably don't want to use yield return, but instead return a List<> or Set, or some other persistent collection instead.

这也是不需要使用收益回报如果你正在处理的查询对象直接。这往往是与LINQ查询的情况下 - 这是更好地只返回的IEnumerable<> 从查询，而不是迭代和收益回报率 ING导致自己。例如：

It's also unnecessary to use yield return if you're dealing with query objects directly. This is often the case with LINQ queries - it's better to just return the IEnumerable<> from the query rather than iterating and yield returning results yourself. For example:

var result = from obj in someCollection
             where obj.Value < someValue
             select new { obj.Name, obj.Value };

foreach( var item in result )
   yield return item; // THIS IS UNNECESSARY....

// just return {result} instead...

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