What’s New in .NET 9: A Comprehensive Comparison with .NET 8

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Microsoft’s recent release of .NET 9 introduces a suite of new features, optimizations, and language improvements designed to enhance the development experience. As an evolution from .NET 8, this update aims to refine runtime performance, streamline cross-platform compatibility, and provide new capabilities for C# developers. In this article, we’ll dive deep into the notable advancements in .NET 9, focusing on its impact on both framework performance and the C# language.

1. Performance Improvements

One of the standout aspects of the .NET 9 update is its attention to performance across a range of areas:

• JIT Compilation: .NET 9 has improved JIT (Just-in-Time) compilation, particularly focusing on methods frequently called with a small number of hot paths. This change reduces the warm-up time, meaning applications can reach peak performance faster. The compiler can now better optimize certain branching patterns, especially within loops, providing smoother performance for workloads with complex conditional logic.
• Garbage Collection Enhancements: Microsoft has made significant refinements to garbage collection (GC) in .NET 9. A major change is the tuning of the GC in high-memory environments, where it now better handles large heaps, reducing memory fragmentation. In workloads with high object allocation, this results in fewer latency spikes, making .NET 9 suitable for applications requiring smoother and more consistent memory management.
• HTTP and Networking: With optimizations to HTTP/2 and HTTP/3, .NET 9 provides better performance for network-heavy applications. Improvements to the HTTP/3 stack have reduced latency for web applications, particularly in real-time and interactive applications.
• Native AOT (Ahead-of-Time Compilation): While .NET 8 introduced AOT, .NET 9 brings further optimizations that minimize application startup time and memory consumption. With improved tooling, developers can now more easily utilize AOT for console applications, ASP.NET Core applications, and microservices, making it more feasible for resource-constrained environments.

2. New and Enhanced Features in ASP.NET Core

ASP.NET Core in .NET 9 has been improved in several key areas:

• Enhanced Middleware Pipeline: The middleware pipeline in ASP.NET Core has been fine-tuned, enabling better concurrency and lower latency. Developers can expect faster responses to incoming requests, especially for complex multi-service architectures.
• Razor Component Libraries: .NET 9 introduces Razor Component Libraries (RCL) with enhanced support for modular components, improving code sharing in Blazor applications. RCLs now provide better support for theming and customization, facilitating easier reuse of UI elements across projects.
• SignalR Enhancements: SignalR has also been improved for real-time applications. .NET 9 enables better client-server communication with lower latency and increased scalability. For applications that rely heavily on bi-directional communication (like chat applications and live dashboards), these enhancements make .NET 9 a more compelling choice.

3. Major Updates to the C# Language in .NET 9

The .NET 9 release brings with it C# 13, introducing features to improve code readability, robustness, and developer productivity.

• Primary Constructors for Records and Structs: C# 13 extends the primary constructor syntax, introduced for records, to structs. This makes immutable structs more accessible and provides a streamlined way to initialize value types, which is especially useful for DTOs (Data Transfer Objects) and small data structures.
• Lambda Expression Enhancements: Lambdas in C# 13 can now have return types and are more flexible in inferring types, making them easier to use in more complex functional-style programming scenarios. This reduces the need for explicit delegate types and makes it easier to write clean, concise functional code.
• Pattern Matching Advancements: Pattern matching has been further extended, introducing features like list patterns and relational patterns, which enhance the capability of handling complex data structures. These new patterns enable developers to write clearer and more concise logic, particularly when working with collections.
• New required Keyword for Properties: Building on the features introduced in C# 11 and 12, C# 13 introduces the required keyword for properties, enforcing the initialization of specific properties at object creation. This is particularly helpful in ensuring that objects are fully initialized before being used, improving runtime safety.

4. Cross-Platform Improvements

With .NET 9, cross-platform support has been expanded further, enhancing development for MacOS and Linux environments.

• Native ARM64 Support on macOS: .NET 9 includes improved support for ARM64 processors on macOS, particularly benefiting developers working on Apple Silicon. This means faster builds, lower resource usage, and improved compatibility with Apple’s latest hardware.
• Enhanced Container Support: Containers are a first-class citizen in .NET 9. This update includes better support for building and running .NET applications within Docker containers, specifically with enhanced multi-stage builds, making it easier to manage dependencies and optimize images for production.
• Platform-Specific Analyzers: Platform-specific analyzers have been introduced to .NET 9, helping developers catch issues that could arise when running code across different OS environments. These analyzers provide compile-time checks to ensure code compatibility, reducing unexpected platform-specific bugs.

5. Libraries and Tools

In addition to the above runtime and framework enhancements, .NET 9 introduces several libraries and tools aimed at improving developer productivity:

• System.Text.Json Improvements: Serialization and deserialization using System.Text.Json have been made faster and more efficient. New features, such as ImmutableArray support and dynamic type handling, provide better flexibility for handling complex JSON payloads.
• Updated Diagnostic Tools: Profiling and debugging in .NET 9 have been enhanced with more detailed diagnostic data. Developers can now better trace memory leaks, analyze performance bottlenecks, and debug concurrency issues, thanks to these new diagnostic capabilities.
• Expanded MAUI Support: .NET Multi-platform App UI (MAUI) continues to evolve, with new controls, better styling options, and enhanced bindings. These updates make it easier to develop cross-platform applications, particularly for developers looking to target mobile and desktop applications with a single codebase.

Summary

.NET 9 is a significant step forward, bringing an array of performance optimizations, new features in ASP.NET Core, and enhanced C# language capabilities. These improvements reinforce Microsoft’s commitment to creating a versatile and performant framework for modern applications. Highlights of this release include:

• Performance improvements in JIT compilation, GC, and AOT
• Enhanced ASP.NET Core, with refined middleware and SignalR support
• New language features in C# 13, such as primary constructors, lambda enhancements, and pattern matching
• Improved cross-platform support, especially for ARM64 on macOS and containerization
• Expanded libraries and diagnostic tools, including updates to System.Text.Json and MAUI

In essence, .NET 9 builds upon the foundations of .NET 8 to deliver a more robust, efficient, and cross-platform framework suitable for a wide range of applications. This release solidifies .NET’s position as a top choice for both enterprise and open-source developers, offering tools and capabilities that cater to the needs of modern software projects.