Linq到对象：TakeWhileOrFirst(Linq to Objects: TakeWhileOrFirst)

Linq到对象：TakeWhileOrFirst(Linq to Objects: TakeWhileOrFirst)

使用linq将以下内容应用于序列的最可读方式是什么？

TakeWhile elements are valid but always at least the first element

编辑：我已经更新了标题，更准确。 我很抱歉有什么困惑，下面的答案肯定会教给我一些东西！

预期的行为是这样的：Take while元素有效。 如果结果是一个空序列，无论如何要采取第一个元素。

What would be the most readable way to apply the following to a sequence using linq:

TakeWhile elements are valid but always at least the first element

EDIT: I have updated the title, to be more precise. I'm sorry for any confusion, the answers below have definitely taught me something!

The expected behavior is this: Take while element are valid. If the result is an empty sequence, take the first element anyway.

最满意答案

据我所知，它可以最有效地手动实现，以确保它不会超过必要的枚举。

public static IEnumerable<TSource> TakeWhileOrFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) { using (var enumerator = source.GetEnumerator()) { if (!enumerator.MoveNext()) yield break; TSource current = enumerator.Current; yield return current; if (predicate(current)) { while (enumerator.MoveNext() && predicate(current = enumerator.Current)) yield return current; } } }

为了完成，包含索引的重载：

public static IEnumerable<TSource> TakeWhileOrFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, int, bool> predicate) { using (var enumerator = source.GetEnumerator()) { if (!enumerator.MoveNext()) yield break; TSource current = enumerator.Current; int index = 0; yield return current; if (predicate(current, index++)) { while (enumerator.MoveNext() && predicate(current = enumerator.Current, index++)) yield return current; } } }

It would be most efficiently implemented manually as far as I can tell to ensure that it isn't enumerated over more than necessary.

public static IEnumerable<TSource> TakeWhileOrFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) { using (var enumerator = source.GetEnumerator()) { if (!enumerator.MoveNext()) yield break; TSource current = enumerator.Current; yield return current; if (predicate(current)) { while (enumerator.MoveNext() && predicate(current = enumerator.Current)) yield return current; } } }

And for the sake of completion, an overload that includes the index:

public static IEnumerable<TSource> TakeWhileOrFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, int, bool> predicate) { using (var enumerator = source.GetEnumerator()) { if (!enumerator.MoveNext()) yield break; TSource current = enumerator.Current; int index = 0; yield return current; if (predicate(current, index++)) { while (enumerator.MoveNext() && predicate(current = enumerator.Current, index++)) yield return current; } } }