C# 12 and .NET 8 Updates

Collection expressions

Chapter 6, Arrays

Collection expressions are a new feature in C# 12. Collection expressions are used to initialize collections. The following code sample shows how to use collection expressions with arrays.

int[] numbers1 = { 1, 2, 3, 4, 5 }; // array initializer
int[] numbers2 = [1, 2, 3, 4, 5]; // collection expression

Chapter 8, Collections

Instead of

    ImmutableArray<string> arr = ImmutableArray.Create<string>("one", "two", "three", "four", "five");

We can do this:

    ImmutableArray<string> arr = ["one", "two", "three", "four", "five"];

Spread operator

Chapter 8, Collections

The spread operator is used to add elements of a collection to another collection. The following code sample shows how to use the spread operator with arrays.

Instead of this:

    ImmutableList<Account> immutableAccounts = accounts.ToImmutableList();

We can do this:

    ImmutableList<Account> immutableAccounts = [.. accounts];

Primary constructor

Chapter 8, Collections

The primary constructor is used to initialize members of a class. The following code sample shows how to use the primary constructor with the ImmutableList<T> class.

Instead of this:

public class RacerComparer : IComparer<Racer>
{
    private CompareType _compareType;
    public RacerComparer(CompareType compareType) =>
      _compareType = compareType;

We can do this:

public class RacerComparer(CompareType compareType) : IComparer<Racer>
{
    private CompareType _compareType = compareType;

Or this (and use the compareType as parameter, access it when needed):

public class RacerComparer(CompareType compareType) : IComparer<Racer>
{

Chapter 24 - ASP.NET Core

• Using primary constructors
• httpContext.Response.Headers.Append instead of httpContext.Response.Headers.Add (which would throw on duplicates)