C#高性能开发之类型系统：从C# 7.0 到C# 14的类型系统演进全景

public (int id, string name) GetPerson()
{
    return (1, "Alice");
}

var person = GetPerson();
Console.WriteLine($"ID: {person.id}, Name: {person.name}");

// 解构
var (id, name) = GetPerson();
Console.WriteLine($"ID: {id}, Name: {name}");

// Span<T> 和 ReadOnlySpan<T>
int[] numbers = [1, 2, 3, 4, 5];
Span<int> span = numbers.AsSpan(1, 3);
span[0] = 10;
Console.WriteLine(string.Join(", ", span.ToArray())); // 10, 3, 4

ReadOnlySpan<char> text = "Hello".AsSpan();
Console.WriteLine(text.Slice(0, 2).ToString()); // He

// 只读结构
readonlystruct Point
{
    publicint X { get; init; }
    publicint Y { get; init; }
}
Point point = new() { X = 1, Y = 2 };
Console.WriteLine($"({point.X}, {point.Y})"); // (1, 2)

// 引用结构
refstruct Buffer
{
    public Span<int> Data;
    public Buffer(Span<int> data) => Data = data;
}
Buffer buffer = new(numbers.AsSpan());
buffer.Data[0] = 10;
Console.WriteLine(numbers[0]); // 10

// 可空引用类型
#nullable enable
string nonNullable = "Hello";
string? nullable = null;
if (nullable != null)
{
    Console.WriteLine(nullable.Length);
}

// Memory<T> 和 ReadOnlyMemory<T>
int[] numbers = [1, 2, 3, 4, 5];
Memory<int> memory = numbers.AsMemory(1, 3);
Span<int> span = memory.Span;
span[0] = 10;
Console.WriteLine(string.Join(", ", memory.ToArray())); // 10, 3, 4

ReadOnlyMemory<char> text = "Hello".AsMemory();
Console.WriteLine(text.Slice(0, 2).Span.ToString()); // He

// 记录
public record Person(string FirstName, string LastName);
var person1 = new Person("Alice", "Smith");
var person2 = new Person("Alice", "Smith");
Console.WriteLine(person1 == person2); // True
var person3 = person1 with { LastName = "Johnson" };
Console.WriteLine(person3); // Person { FirstName = Alice, LastName = Johnson }

// 本机大小整数
nint nativeInt = 42;
nuint nativeUInt = 42u;
Console.WriteLine($"Native int: {nativeInt}, Native uint: {nativeUInt}");

// 初始化器专用类型
publicclassStudent
{
    publicstring Name { get; init; }
}
var student = new Student { Name = "Alice" };
Console.WriteLine(student.Name); // Alice

// 记录结构
public record struct Point(int X, int Y);
var point1 = new Point(1, 2);
var point2 = new Point(1, 2);
Console.WriteLine(point1 == point2); // True
var point3 = point1 with { X = 3 };
Console.WriteLine(point3); // Point { X = 3, Y = 2 }

// 全局 using（假设已在文件顶部）
Console.WriteLine("Hello, World!"); // 无需显式 using System

// 必需成员
publicclassPerson
{
    public required string Name { get; set; }
}
var person = new Person { Name = "Alice" };
Console.WriteLine(person.Name); // Alice

// 泛型数学支持
publicinterfaceINumber<T> whereT : INumber<T>
{
    static abstract T Add(T left, T right);
}
publicreadonlystruct MyNumber : INumber<MyNumber>
{
    publicint Value { get; init; }
    public MyNumber(int value) => Value = value;
    public static MyNumber Add(MyNumber left, MyNumber right) => new(left.Value + right.Value);
}
MyNumber a = new(1);
MyNumber b = new(2);
var result = MyNumber.Add(a, b);
Console.WriteLine(result.Value); // 3

// 文件局部类型
file classHelper
{
    public static void Log(string message) => Console.WriteLine(message);
}
Helper.Log("Test");

[InlineArray(length)]
public struct StructName
{
    private elementType _element0;
}

[InlineArray(10)]
public struct Buffer
{
    private int _element0;
}
Buffer buffer = new();
buffer[0] = 1;
buffer[9] = 10;
Console.WriteLine(buffer[0]); // 1

// 参数集合扩展
public void Process(params Span<int> spans)
{
    foreach (var span in spans)
        Console.WriteLine(string.Join(", ", span.ToArray()));
}
int[] numbers = [1, 2, 3];
Process(numbers.AsSpan(0, 2), numbers.AsSpan(2, 1)); // 1, 2 和 3

// 引用结构接口支持
publicinterfaceIBuffer
{
    void Process();
}
refstruct Buffer : IBuffer
{
    public Span<int> Data;
    public Buffer(Span<int> data) => Data = data;
    public void Process() => Data[0] = 10;
}
Buffer buffer = new(numbers.AsSpan());
buffer.Process();
Console.WriteLine(numbers[0]); // 10

// 部分属性
publicpartialclassPerson
{
    publicpartialstring Name { get; set; }
}
publicpartialclassPerson
{
    publicpartialstring Name { get => _name; set => _name = value; }
    privatestring _name;
}
var person = new Person { Name = "Alice" };
Console.WriteLine(person.Name); // Alice

public class Person
{
    public string Name
    {
        get => field;
        set => field = value?.Trim();
    }
}
var person = new Person { Name = " Alice " };
Console.WriteLine(person.Name); // Alice

Span<int> span = new int[] {1, 2, 3};
int[] array = span.ToArray();
Console.WriteLine(string.Join(", ", array)); // 1, 2, 3

string listName = nameof(List<>);
Console.WriteLine(listName); // List

var increment = (ref int x) => x++;
int num = 5;
increment(ref num);
Console.WriteLine(num); // 6

// File1.cs
publicpartialclassMyClass
{
    public partial MyClass(int x);
    publicpartialevent EventHandler MyEvent;
}

// File2.cs
publicpartialclassMyClass
{
    public partial MyClass(int x) { }
    publicpartialevent EventHandler MyEvent;
}

string? text = null;
text?.Length = 5; // 不执行赋值

List<int>? list = null;
list?[0] = 10; // 不执行赋值

list = new List<int> { 0 };
list?[0] = 10; // 执行赋值，list[0] = 10
Console.WriteLine(list[0]); // 10