GetEnumerator使用

internal class Program
{
    static async Task Main(string[] args)
    {
        var list = new List<int>()
        {
            1, 2, 3, 4, 5, 6, 7,
        };

        var res = Pairwise<int, string>(list, (s1, s2) =>
        {
            return $"{s1}:{s2}";
        });

        foreach (var item in res)
        {
            Console.WriteLine(item);
        }
    }

    public static IEnumerable<TResult> Pairwise<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TSource, TResult> resultSelector)
    {
        using var e = source.GetEnumerator();

        if (!e.MoveNext()) yield break;

        var previous = e.Current;
        while (e.MoveNext())
        {
            yield return resultSelector(previous, e.Current);
            previous = e.Current;
        }
    }
}

输出