Any

namespace System.Linq
{
    public static class Enumerable
    {
        public static bool Any<TSource>(this IEnumerable<TSource> source)
        {
            if (source == null) throw Error.ArgumentNull("source");
            using (IEnumerator<TSource> e = source.GetEnumerator())
            {
                if (e.MoveNext()) return true;
            }
            return false;
        }

        public static bool Any<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 true;
            }
            return false;
        }


        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);
        }
    }
}

 

改进Any

public static class EnumerableExtensions
{

    #region Any

    public static bool HasAny<TSource>(this IEnumerable<TSource> source)
    {
        if (source == null) { return false; }

        using (IEnumerator<TSource> e = source.GetEnumerator())
        {
            if (e.MoveNext()) return true;
        }

        return false;
    }

    public static bool HasAny<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
    {
        if (source == null || predicate == null) { return false; }

        foreach (var item in source)
        {
            if (predicate(item)) return true;
        }

        return false;
    }

    #endregion

    /// <summary>
    /// 遍历列表时不用再判断列表或数组是否为null
    /// eg: foreach (var item in list.CheckNull()) { }
    /// </summary>
    public static IEnumerable<T> CheckNull<T>(this IEnumerable<T> list)
    {
        return list == null ? new List<T>(0) : list;
    }
}