只讀成員 private struct Point { public Point(double x, double y) { X = x; Y = y; } private double X { get; set; } private double Y { get; set; } private r ...
只讀成員
private struct Point { public Point(double x, double y) { X = x; Y = y; } private double X { get; set; } private double Y { get; set; } private readonly double Distance => Math.Sqrt(X * X + Y * Y); public override readonly string ToString() => $"({X}, {Y}) is {Distance} from the origin"; }View Code
使用readonly修飾tostring方法，表示它不可修改
預設介面方法
/// <summary> /// 預設介面方法 /// </summary> private interface IWork { public void Work() { Console.WriteLine("Work"); } }
現在可以在介面中定義預設的方法，而不是只能申明void Work();
更多的模式匹配
使用switch表達式的模式匹配
public enum Rainbow { Red, Orange, Yellow, Green, Blue, Indigo, Violet } //switch表達式 public static Color FromRainbow(Rainbow colorBand) => colorBand switch { Rainbow.Red => Color.Red, Rainbow.Orange => Color.Orange, Rainbow.Yellow => Color.Yellow, Rainbow.Green => Color.Green, Rainbow.Blue => Color.Blue, Rainbow.Indigo => Color.Indigo, Rainbow.Violet => Color.Violet, _ => throw new ArgumentException(message: "invalid enum value", paramName: nameof(colorBand)), };View Code
在變數後面使用switch關鍵字，同時將case:替換為=>，使用_替代default
屬性模式
public static decimal ComputeSalesTax(Address location, decimal salePrice) => location switch { { State: "WA" } => salePrice * 0.06M, { State: "MN" } => salePrice * 0.075M, { State: "MI" } => salePrice * 0.05M, // other cases removed for brevity... _ => 0M }; public struct Address { public string State { get; set; } }View Code
對location變數的State屬性進行模式匹配
元組模式
public static string RockPaperScissors(string first, string second) => (first, second) switch { ("rock", "paper") => "rock is covered by paper. Paper wins.", ("rock", "scissors") => "rock breaks scissors. Rock wins.", ("paper", "rock") => "paper covers rock. Paper wins.", ("paper", "scissors") => "paper is cut by scissors. Scissors wins.", ("scissors", "rock") => "scissors is broken by rock. Rock wins.", ("scissors", "paper") => "scissors cuts paper. Scissors wins.", (_, _) => "tie" };View Code
位置模式
//位置模式，使用解構將屬性解構的離散變數，如果可以訪問 Deconstruct 方法，就可以使用位置模式 檢查對象的屬性並將這些屬性用於模式 public class XPoint { public int X { get; set; } public int Y { get; set; } public void Deconstruct(out int x, out int y) { x = X; y = Y; } } public int GetNumber(XPoint point) => point switch { (0, 0) => 0, var (x, y) when x > 0 && y > 0 => 1, var (x, y) when x < 0 && y > 0 => 2, var (x, y) when x < 0 && y < 0 => 3, var (x, y) when x > 0 && y < 0 => 4, var (_, _) => -1, _ => -2 };View Code
using申明
/// <summary> /// using 聲明，using 表達式的操作數可以實現 IDisposable 或 IAsyncDisposable /// </summary> public void UsingStatement() { using var file = new System.IO.StreamWriter("WriteLines2.txt"); }
可以對非同步可釋放類型使用using關鍵字進行釋放
靜態本地函數
/// <summary> /// 靜態本地函數，在本地函數中使用static關鍵字 /// </summary> private class StaticLocalFunction { int N() { int y; LocalFunction(); return y; void LocalFunction() => y = 0; } int M() { int y = 5; int x = 7; return Add(x, y); static int Add(int left, int right) => left + right; } }View Code
可以在本地函數申明中使用static關鍵字
索引和範圍
private class IndexRange { string[] words = new string[] { // index from start index from end "The", // 0 ^9 "quick", // 1 ^8 "brown", // 2 ^7 "fox", // 3 ^6 "jumped", // 4 ^5 "over", // 5 ^4 "the", // 6 ^3 "lazy", // 7 ^2 "dog" // 8 ^1 }; // 9 (or words.Length) ^0 void Test() { //>=index_1 && < index_4 var quickBrownFox = words[1..4]; var lazyDog = words[^2..^0]; } }View Code
null合併賦值
/// <summary> /// null合併賦值 /// </summary> private void NullMergeAssignment() { List<int> list = new List<int>(); List<int> numbers = list.Where(x => x > 20).ToList(); numbers ??= new List<int>(); }
當左操作數計算為 null 時，將??= 右操作數的值分配給左操作數
非同步流
public static class AsyncStream { public static async System.Collections.Generic.IAsyncEnumerable<int> GenerateSequence() { for (int i = 0; i < 20; i++) { await Task.Delay(100); yield return i; } } public static async void GetNumbers() { var c = CSharp8.AsyncStream.GenerateSequence(); await foreach (var number in c) { Console.WriteLine(number); } } }View Code
GetNumbers使用await等待返回結果，每隔100ms會輸出i++的值
