根据委托和lamdba表达式扩展方法

1. lamdba表达式ForEach扩展方法：

 public static void GetForEach<T>(this IEnumerable<T> list, Action<T> action)
        {
            foreach (var da in list)
            {
                //输出
                action(da);
            }
        }

2.lamdba表达式Where扩展方法：

 public static IEnumerable<T> GetWhere<T>(this IEnumerable<T> list, Func<T, bool> action)
        {
            List<T> tlist = new List<T>();
            foreach (var da in list)
            {
                Console.WriteLine(action(da));
                if (action(da))
                {
                    tlist.Add(da);
                }
            }
            return tlist;
        }

3.lamdba表达式FirstOrDefault扩展方法：

 public static T GetFirstOrDefault<T>(this IEnumerable<T> list, Func<T, bool> func)
        {
            T t = default(T);
            foreach (T da in list)
            {
                if (func(da))
                {
                    return da;
                }
            }
            return t;
        }