linq-First
源码:
public static TSource First<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) throw Error.ArgumentNull("source"); if (predicate == null) throw Error.ArgumentNull("predicate"); foreach (TSource element in source) { if (predicate(element)) return element; } throw Error.NoMatch(); } public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source) { if (source == null) throw Error.ArgumentNull("source"); IList<TSource> list = source as IList<TSource>; if (list != null) { if (list.Count > 0) return list[0]; } else { using (IEnumerator<TSource> e = source.GetEnumerator()) { if (e.MoveNext()) return e.Current; } } return default(TSource); } public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) throw Error.ArgumentNull("source"); if (predicate == null) throw Error.ArgumentNull("predicate"); foreach (TSource element in source) { if (predicate(element)) return element; } return default(TSource); }