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What is the new in C#11?

article 2024/11/15 5:59:37

Raw String Literals

List Pattern

Slice Pattern

Var Pattern

File Local Types

Required Members

Auto Default Structs

Ref Fields

Raw String Literals

"""里面的内容是space敏感的。意思是如果”age”前面有几个空格，就会打印几个空格。

/*
{
    "name":"Evan",
    "age": 37
}
 */

//older than C#11
string json = "{\r\n    \"name\":\"Evan\",\r\n    \"age\": 37\r\n}";
//C#11 new feature
string json2 = """
        {
        "name":"Evan",
        "age": 37
        }
    """;
//“age”前面的space数量与最下面的"""空格数量不一致，会编译报错
string json_Error = """
        {
    "name":"Evan",
"age": 37
        }
    """;

List Pattern

/*
 * RUle 1: should contains only 2 elements
 * Rule 2: The element 0 should be 10
 * Rule 3: The element 1 should be less than 25
 * RUle 4: The element 2 should be equals 50 and 60
 * 
*/
int[] values = { 10, 20, 60 };

//older
bool verify1 = values.Length == 3 && values[0] == 10 && values[1] < 25 && (values[2] == 50 || values[2] == 60);

//New in C# 11
bool verify2 = values is [10, < 25, 50 or 60];

Slice Pattern

Console.WriteLine(new List<int> { 10, 20, 60 } is [10, < 25, 50 or 60]);//True
Console.WriteLine(new List<int> { 10, 20, 30, 60 } is [10, < 25, _, 50 or 60]);//True. _ 代表index=2的位置
Console.WriteLine(new List<int> { 10, 20, 30, 60, 70, 80 } is [10, < 25,.., 50 or 80]);//True. ..代表 30, 60, 70
Console.WriteLine(new List<int> { 10, 20, 30, 60, 24, 80 } is [.., < 25,  50 or 80]);//True. ..代表 10, 20, 30, 60, 
Console.WriteLine(new List<int> { 10, 20, 30, 60, 24, 80 } is [10, < 25, ..]);//True. ..代表 30, 60, 24, 80

//Console.WriteLine(new List<int> { 10, 20, 30, 60, 24, 80 } is [10,.., < 25, ..]);//Compiler error

Var Pattern

Console.WriteLine(new List<int> { 10, 20, 60 } is [10, var a, var b] && (a == 20 && b == 60));
Console.WriteLine(new List<int> { 10, 20, 60 } is [10, var x and >= 20, var y] && y == 60);

var person = new Person("Evan", "Wang", 37);
Console.WriteLine(person is ("Evan", "Wang", > 35));//true
Console.WriteLine(person is ("Zhen", "Wang", 37));//false
Console.WriteLine(person is ("Zhen", "Wang", 37) and var (firstName, lastName, age) && age >= 35);//true

File Local Types

个人感觉没啥用，internal class可以代替这个class，唯一不用的是internal class是libarary内部级别的，file class是文件级别的(即只有相同文件里面可以引用)。

//Program.cs
TestFileClass test = new TestFileClass();
test.Print();//Print: ABC AdditionalTestFileClass

//var fileClass = new AdditionalTestFileClass();//Compiler error


//TestFileClass.cs
    internal class TestFileClass
    {
        public void Print()
        {
            var value = new AdditionalTestFileClass().GetAdditinalPrint();
            Console.WriteLine($"ABC {value}");
        }
    }

    file class AdditionalTestFileClass
    {
        public string GetAdditinalPrint()
        {
            return "AdditionalTestFileClass";
        }
    }

Required Members

    public class RequiredDemo
    {
        public required string Name { get; set; }
    }


//var c1=new RequiredDemo();//Compile time Error: you must initialize the required property

var c2=new RequiredDemo() {Name="Evan"};//set value for required property

Auto Default Structs

public struct Point  
{  
    public int X;  
    public int Y;  
  
    // 构造函数（可选）  
    public Point(int x, int y)  
    {  
        X = x;  
        Y = y;  
    }  
  
    // 无参数的构造函数（可选，但在结构体中不常见）  
    // public Point() { } // 这将允许Point p = new Point(); 但通常不需要  
}  
  
// 使用  
Point p1 = new Point(1, 2); // 使用构造函数显式初始化  
Point p2 = default(Point); // 使用default关键字获取默认实例  
Point p3 = new Point(); // 如果没有定义无参数构造函数，这将是一个编译错误  
// 但如果你确实定义了无参数构造函数，则上面的代码是有效的，但通常不推荐这样做，因为默认(Point)已经足够了  
  
// C# 7.1+ 可以使用目标类型新表达式  
Point p4 = new(); // 仅当结构体定义了无参数构造函数时有效，或者使用了编译器对default的改进

Ref Fields

Limitation:

A ref struct can't be the element type of an array.
A ref struct can't be a type of a field of a class or non-ref struct
A ref struct can't impement interfaces
A ref struct can't be boxed to System.ValueType of System.Object
A ref struct can't be a type argument for generic (泛型)types or generic methods.
A ref struct variable can't be captured in a lambda expression or a local function.
Before C#13, ref struct variables can't be used in an async method.
Beignning with C#13, ref struct variables canbe used until "await" keyword apprears..

int value = 37;
StructA a = new StructA();
a.filed = value;

RefStructA refA = new RefStructA(ref value);

Console.WriteLine($"a=={a.filed}");//a==37;
Console.WriteLine(value);//37;
Console.WriteLine($"ref a=={refA.filed}");//ref a==37;

value = 18;
Console.WriteLine($"a=={a.filed}");//a==37;
Console.WriteLine(value);//18;
Console.WriteLine($"ref a=={refA.filed}");//ref a==18;

public struct StructA
{
    public int filed;
}

public ref struct RefStructA
{
    public ref int filed;
    public RefStructA(ref int a)
    {
        filed = ref a;
    }
}

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