[Home](../) › [Blog](../blog) › Metalama 2025.0 Generally Available: Support for C# 13 and .NET 9, Aspect Framework Improvements, and More # Metalama 2025.0 Generally Available: Support for C# 13 and .NET 9, Aspect Framework Improvements, and More > Announcing the general availability of Metalama 2025.0: support for C# 13, .NET 9, Roslyn generators and interceptors; many improvements in the aspect framework; nearly doubled performance; async and background WPF commands. Published: 2025-01-04 · Author: Gaël Fraiteur · Canonical: https://postsharp.net/blog/metalama-2025-0-ga Metalama 2025.0 is now generally available! This release supports C# 13 and .NET 9, adds significant enhancements to the aspect framework, and nearly doubles performance. This article highlights the most significant improvements. For a detailed discussion, see the [release notes](https://doc.metalama.net/conceptual/release-notes/release-notes-2025-0) of Metalama 2025.0. Note that we are simultaneously releasing [PostSharp 2025.0](https://postsharp.net/blog/postsharp-2025-0-ga). ## C# 13 and .NET 9 The primary goal of Metalama 2025.0 is to support the new .NET stack. All new C# features and the new .NET SDK have been implemented and tested. This includes: - `params` collections - `ref`/`unsafe` in iterators and async methods - `ref struct` can implement interfaces - Classes can have `ref struct` constraints - New escape character in strings - Locking on the `Lock` class - Implicit indexer access in object initializers - Overload resolution priority - `partial` properties We've updated third-party dependencies. Note that the minimum supported version of Visual Studio is now 17.6 LTSC (Roslyn 4.4). ## Support for code generators and interceptors We've improved the integration of Metalama with code generators and interceptors. We now consistently execute source generators _after_ any Metalama transformation. This approach has three benefits: - It offers a consistent experience both at design time and build time. - Aspects can introduce code that relies on code generators, such as the `[GeneratedRegex]` attribute. - You can now use Roslyn interceptors alongside Metalama since they no longer conflict with our code transformations. The downside is that you can no longer use Metalama aspects in Razor (`.cshtml`) pages. ## Aspect framework improvements - **Closing gaps with introduced types.** You can now use introduced types in type constructs like `Foo[]`, `List`, `Foo`, or `Foo*`, where `Foo` is the introduced type. - **Introduction of static virtual, abstract, and partial members.** We've lifted several limitations in member introductions. - **Introduction of generic interfaces.** You can now implement a generic interface without limitation. Previously, for a class `Bar`, it was impossible to implement an interface `IFoo`, which was crucial to implement, for instance, comparison patterns. - **Introduction of extension methods.** You can now introduce extension methods by adding the `[This]` attribute to the first parameter of the template method or setting the `IParameterBuilder.IsThis` property. - **Dynamic definition of local variables.** You can now dynamically define a local variable in a T# template thanks to the new `meta.DefineLocalVariable` method, which returns an `IExpression`. - **Suppression of well-known warnings in aspects.** We now suppress some compiler warnings in aspect code because they are generally irrelevant given the meta-programming nature of the code. - **Clean-up of IRef and overridden field representation.** We've refactored the implementation (and, to some extent, the public API) of the `IRef` interface and made the representation of overridden fields more consistent. ## Async and background WPF commands The `[Command]` aspect now supports asynchronous and background commands: - Asynchronous commands are those that return a `Task`. - Background commands, whether synchronous or not, execute in a background thread instead of the UI thread. Both asynchronous and background commands can be canceled through a `CancellationToken` parameter. Thanks to extensive refactoring of the code model and other efforts, Metalama 2025.0 is almost twice as fast as 2024.2 under a typical workload. The overhead of Metalama 2025.0 is about 60% of the overhead of the previous version. You should now find your builds are between 25% and 35% slower with Metalama than without it, depending on the number of aspects. At 25% to 35% overhead, performance should no longer be a concern when adopting Metalama. For precise measurements and methodology, see [this blog post](https://postsharp.net/blog/metalama-performance). ## Bug fixes We fixed 43 bugs in this release, most of them affecting the design-time experience. We are monitoring telemetry data to identify and prioritize remaining issues. ## Breaking changes As noted above, we've updated all third-party dependencies to their latest versions. Also, the minimum supported version of Visual Studio is now 17.6 LTSC (Roslyn 4.4). Additionally, we must declare a few breaking changes in the public API of `IRef` and `Metalama.Patterns.Commands`. For details, see the [release notes](https://doc.metalama.net/conceptual/release-notes/release-notes-2025-0#breaking-changes) ## Conclusion Metalama 2025.0 is a strong release from several angles. It is a platform update, and it also closes most feature gaps in the aspect framework and nearly doubles performance. Note that implementing these improvements required extensive refactoring of the code model. As a result, we may have destabilized some use cases that were not covered by any tests. Please be careful when updating to 2025.0 (i.e., don't do it in a rush), and don't hesitate to report any issues. We're looking forward to your feedback. Happy meta-programming with Metalama! --- ## Site navigation - Index of the whole site: [llms.txt](../llms.txt)