1 void Foo(int? num)
2 {
3     if (!num.HasValue)
4      /* null logic */
5     else if (num.Value > 0)
6      /* positive int logic */
7     else
8      /* negative int & zero logic */
9 }

View Code

 1 Sub Foo(Num As Integer?)
 2     Select Case Num
 3         Case Not Num.HasValue
 4         'null logic
 5         Case Num > 0
 6         'positive Int logic
 7         Case Num <= 0
 8             'negative Int() & zero logic
 9         Case Else
10
11     End Select
12 End Sub

View Code

 1 void Foo(int? num)
 2 {
 3     switch (num)
 4     {
 5         case null:
 6             //null logic
 7             break;
 8         case int n when n > 0:
 9             //positive Int logic
10             break;
11         case int n when n <= 0:
12             //negative Int() & zero logic
13             break;
14     }
15 }

var reuslt = x == null ? default(int) : (x is Func<int> ? (x as Func<int>)() : (x is int ? Convert.ToInt32(x) : default(int)));

var result = x match(case Func<int> f: f(),case int i: i,case *: default(int)
);

 1 class Device
 2 {
 3     public ProductLineOption ProductLine { get; set; }
 4 }
 5
 6 class MobiePhone : Device
 7 {
 8     public string IMEICode { get; set; }
 9 }
10
11 IEnumerable<Device> GetAllDevices() { /* 获取并返回所有设备 */ };
12
13 IEnumerable<string> GetAlliPhoneIMEI()
14 {
15     var deviceList = this.GetAllDevices();
16     foreach (Device device in deviceList)
17     {
18         MobiePhone phone = device as MobiePhone;
19         if (phone == null) continue;
20
21         if (phone.ProductLine == ProductLineOption.IPhone)
22         {
23             yield return phone.IMEICode;
24         }
25     }
26 }

 1 IEnumerable<string> GetAlliPhoneIMEI()
 2 {
 3     List<Device> deviceList = this.GetAllDevices();
 4     foreach (Device device in deviceList)
 5     {
 6         if (device is MobiePhone { IMEICode is var imei, ProductLine is ProductLineOption.IPhone})
 7         {
 8             yield return imei;
 9         }
10     }
11 }

 1 abstract class Animal
 2 {
 3     public string Name { get; set; }
 4 }
 5
 6 class Dog : Animal
 7 {
 8     public string BarkLikeCrazy() => "WOOF WOOF WOOF";
 9 }
10
11 class Cat : Animal { }
12 class Swan : Animal { }
13
14 class Program
15 {
16     static void Main(string[] args)
17     {
18         var animals = new Animal[] {
19             new Dog { Name = "hola" },
20             new Cat { Name = "tom" },
21             new Swan { Name = "hacienda" }
22         };
23
24         var organizedAnimals = from animal in animals
25                                let sound = animal match( //Match语句
26                                    case Dog d: "woof... " + d.BarkLikeCrazy(), //类型匹配
27                                    case Cat c: "meow",
28                                    case * : "I'm mute.." //通配符匹配
29                                )
30                                select new { Type = animal, Sound = sound };
31
32         foreach (var animal in organizedAnimals)
33         {
34             Console.WriteLine($"{animal.Type.ToString()} - {animal.Sound}");
35         }
36
37         foreach (var a in animals)
38         {
39             if (a is Cat { Name is var name }) //类型及属性匹配，is表达式
40             {
41                 Console.WriteLine($"Name of {nameof(Cat)} is {name}");
42             }
43
44             string sound = "";
45             switch (a) //匹配switch语句
46             {
47                 case Dog d when d.Name == "hola":
48                     sound = "woof... hola" + d.BarkLikeCrazy();
49                     break;
50                 case Dog d:
51                     sound = "woof..." + d.BarkLikeCrazy();
52                     break;
53                 case Cat c:
54                     sound = "meow";
55                     break;
56                 case IEnumerable<Animal> l when l.Any():
57                     //TODO: any logic;
58                     break;
59                 case null:
60                     sound = "no animal";
61                     break;
62                 default:
63                     sound = "I'm mute..";
64                     break;
65             }
66             Console.WriteLine($"{a.ToString()} - {sound}");
67         }
68     }
69 }