New Features .NET 9 and C# 13: What Developers Need to Know

New Features .NET 9 and C# 13: What Developers Need to Know

.NET 9 introduces several significant enhancements across its runtime, libraries, and ASP.NET Core framework. The runtime now features a new attribute model for feature switches, enabling libraries to toggle functionalities effectively. Performance improvements, such as dynamic garbage collection and loop optimizations, enhance application efficiency.

In the libraries, System.Text.Json supports nullable reference types and allows for customized JSON formatting. New LINQ methods, CountBy and AggregateBy, facilitate efficient data aggregation without unnecessary allocations. The PriorityQueue<TElement, TPriority> type has been enhanced with a method to update item priorities seamlessly.

ASP.NET Core benefits from improved security, optimized static file handling, and enhanced support for OpenAPI document generation. Additionally, new templates for Blazor applications and better monitoring capabilities contribute to a more robust development experience. Overall, .NET 9 emphasizes performance, security, and developer productivity, making it a compelling upgrade for .NET developers.

.NET 9 Features

Runtime Enhancements

The new attribute model for feature switches allows libraries to toggle functionality easily. For example:

[FeatureSwitch("NewFeature")]
public void SomeMethod() { /* Implementation */ }

Garbage Collection

Dynamic adaptation to application size improves memory management automatically.

System.Text.Json

Supports nullable reference types and allows customization of JSON indentation:

var options = new JsonSerializerOptions { WriteIndented = true };

LINQ Enhancements

New methods like CountBy and AggregateBy streamline data aggregation:

var result = items.CountBy(x => x.Category);

ASP.NET Core Improvements

Enhanced security and performance, including optimized static file handling and built-in OpenAPI support.

C# 13 Features

C# 13, part of the .NET 9 SDK, brings a host of new features that improve both functionality and usability. Here are some key highlights:

Raw String Literals

Simplifies multi-line string handling:

var json = """
{
    "key": "value"
}
""";

Required Members

Enforces initialization of certain properties:

public class Person
{
    public required string Name { get; init; }
}

Params Collections

You can now use params with collections, allowing for more flexible method signatures.

public void ProcessItems(params List<string>[] items) { /* Implementation */ }

New Lock Type and Semantics

A refined locking mechanism enhances thread safety.

lock (new object()) { /* Critical section */ }

New Escape Sequence - \e

This allows for easier string formatting.

string message = "This is an escape sequence: \e";

Method Group Natural Type Improvements

Simplifies method group conversions.

Implicit Indexer Access in Object Initializers

You can now initialize collections more intuitively.

var dict = new Dictionary<string, int> { ["key"] = 1 };

Ref Locals and Unsafe Contexts in Iterators

Enhances performance in asynchronous programming.

Ref Struct Types Implementing Interfaces

Increases flexibility in struct usage.

Partial Properties and Indexers

Allows for better organization in partial classes.

Overload Resolution Priority

Library authors can now specify preferred overloads.

Field Backed Properties

Introduces a new way to define properties.

These features collectively enhance the language’s expressiveness and performance, making C# 13 a significant update for developers.

Resource

Breaking changes in .NET 9
https://learn.microsoft.com/en-us/dotnet/core/compatibility/9.0

What’s new in .NET 9
https://learn.microsoft.com/en-us/dotnet/core/whats-new/dotnet-9/overview

What’s new in C# 13
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-13