Csharp 8

Liens

• What's new in C# 8.0
• C# language versioning

Switch expression

string myVar; switch (i) { case 1: myVar = "One"; default: throw new ArgumentOutOfRangeException(nameof(i)); } var myVar = i switch { 1 => "One", _ => throw new ArgumentOutOfRangeException(nameof(i)) };

Using declaration

using (var file = new StreamWriter("MyFile.txt")) { // some code } // file is disposed here void MyMethod() { using var file = new StreamWriter("MyFile.txt"); // some code // file is disposed here, at the end of the enclosing scope }

Static local function

int x = 5; int y = 7; return Add(x, y); // Can be static because it doesn't access any variables in the enclosing scope static int Add(int left, int right) => left + right;

Asynchronous streams / async yield

public static async IAsyncEnumerable<int> GenerateSequence() { for (int i = 0; i < 20; i++) { await Task.Delay(100); yield return i; } } await foreach (var number in GenerateSequence()) { Console.WriteLine(number); }

Indices and ranges

var latest = myList[^1]; var secondToFour = myList[2..5]; var lastTwo = myList[^2..^0]; var firstThree = myList[..4]; var allExceptFirst = myList[2..];

Null-coalescing assignment / ?? =

int? i = null; i = i == null ? 20 : i; i = i ?? 20; i ??= 20; // assign 20 to i if i is null

Nullable reference type

MyProject.csproj

<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <TargetFramework>netcoreapp3.1</TargetFramework> <!-- add this line to enable it --> <Nullable>enable</Nullable>

Now by default everything is non nullable. If you want to declare a type as accepting null values, you need to add ? after the type.

string s1 = null; // Warning: Converting null literal or possible null value to non-nullable type. string? s2 = null; // ok // null-forgiving operator Console.WriteLine(s2!.Length); // in this case we know that s2 is not null, so we can use "!" to instruct the compiler "s2" is not null here // allow null even if the type is not nullable public void MyMethod([AllowNull]ref string value) { } // disallow null even if the type is nullable public void MyMethod([DisallowNull]ref string? value) { } private string s1 = ""; // allow null for setter even if the type is not nullable [AllowNull] public string S1 { get => s1; set => s1 = value ?? ""; }

.NET Framework

The C# 8 / .NET Framework combination is not officially supported by Microsoft.
It can be forced by editing the csproj file.

MyProject.csproj

<?xml version="1.0" encoding="utf-8"?> <Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"> <PropertyGroup> <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion> <LangVersion>8.0</LangVersion>

• default interface members won't work
• asynchronous streams and indices and ranges will need polyfill nuget package