Liens

Switch expression

switch (i)
{
    case 1:
        return "One";
    default:
        throw new Exception("Invalid value");
}

i switch
{
    1 => "One",
    _ => throw new Exception("Invalid value")
};

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

Nullable reference types

MyProject.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <Nullable>enable</Nullable>

.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
ssynchronous streams and indices and ranges will need polyfill nuget package