Func

 Func<List<int>, string> getStr = (list) =>
                {
                    var returnStr = "";
                    if (list.Any())
                    {
                        list.ForEach(o => returnStr += o);
                    }
                    return returnStr;
                };

• Func<T1,T2> T1为输入参数,T2为输出参数