C# Func入门二

这一篇是继续上篇的，只不过这篇用的数据是个对象。

一、这边要构建的数据如下：

1.User类

 public class User
    {
        public int identity { get; set; }
        public string name { get; set; }
        public string city { get; set; }
        public string birth { get; set; }
        public User(int id, string n, string c, string bir)
        {
            identity = id;
            name = n;
            city = c;
            birth = bir;
        }
    }

2.返回全部测试的User数据如下

public static User[] GetAllUsers()
        {

            User[] users =
            {
              new User(1, "John", "London", "2001-04-01"),
              new User(2, "Lenny", "New York", "1997-12-11"),
              new User(3, "Andrew", "Boston", "1987-02-22"),
              new User(4, "Peter", "Prague", "1936-03-24"),
              new User(5, "Anna", "Bratislava", "1973-11-18"),
              new User(6, "Albert", "Bratislava", "1940-12-11"),
              new User(7, "Adam", "Trnava", "1983-12-01"),
              new User(8, "Robert", "Bratislava", "1935-05-15"),
              new User(9, "Robert", "Prague", "1998-03-14"),
            };
            return users;
        }

二、例子八：筛选出住在"Bratislava"的人。

//8.c# Func filter array
        static void FunFilterArray()
        {
            var users = GetAllUsers();
            var city = "Bratislava";
            Func<User, bool> livesIn = e => e.city == city;
            var res = users.Where(livesIn);
            foreach (var t in res)
            {
                Console.WriteLine(t.name);
            }
        }

测试结果如下：

 三、例子九：筛选出年龄大于60岁的人。

 //9.c# Func filter by age
        public static int GetAge(User user)
        {
            var dob = DateTime.Parse(user.birth);
            return (int)Math.Floor((DateTime.Now - dob).TotalDays / 365.250);
        }
        public static void FuncFilterByAge()
        {
            var users = GetAllUsers();
            var age = 60;
            Func<User, bool> olderThan60 = e => GetAge(e) > age;
            var res = users.Where(olderThan60);
            foreach (var e in res)
            {
                Console.WriteLine(e.name);
            }

        }

 四、例子十：Func也可以当作一个参数。（可以与例子八的写法比较一下）

 //10.c# pass Func as parameter
        public static void ShowOutPut(User[] users, Func<User, bool> condition)
        {
            var data = users.Where(condition);
            foreach (var person in data)
            {
                Console.WriteLine(person.name);
            }
        }
        public static void FuncAsParameter()
        {
            var users = GetAllUsers();
            ShowOutPut(users, r => r.city == "Bratislava");
        }

测试结果如下：

 五、例子十一：我们可以通过链接来编写Funcs。

 //11.C# Func compose.(We can compose Funcs by chaining.)
        public static void FuncChaining()
        {
            var vals = new int[] { 1, 2, 3, 4, 5 };
            Func<int, int> inc = e => e + 1;
            Func<int, int> cube = e => e * e * e;
            var res = vals.Select(inc).Select(cube);
            foreach (var e in res)
            {
                Console.WriteLine(e);
            }
        }

测试结果如下：

 六、网址参考

https://zetcode.com/csharp/func/

本地代码在CSharpBasic\FuncTutorial