Project "Caravela" 0.1 / / Caravela Documentation / Conceptual Documentation

PostSharp "Caravela"


You can try PostSharp "Caravela" in your browser, without installing anything, at

Table of contents

See also


PostSharp "Caravela" is an extension of the Microsoft "Roslyn" C# compiler that allows you to automatically transform your source code at build time (and, in the future, design time) based on encapsulated code transformations called aspects. PostSharp "Caravela" can be used for aspect-oriented programming, but is not limited to it.

PostSharp "Caravela" is intended to replace the MSIL-based technology stack that is now the foundation of PostSharp and its copies.


PostSharp "Caravela" is currently released under the terms of the Evaluation License of PostSharp.

Caravela is currently in EARLY PREVIEW stage and is not intended for commercial use. Any version of the Caravela preview will stop working 90 days after it has been built. To continue using it, you will need to update to a newer preview.


To see Caravela in action, go to

You can also look at the following repos for example:

  • Caravela.Samples: a set of examples built using the Caravela aspect framework. Includes:

    • Logging (of course!)
    • Caching
    • Auto-retry
  • Caravela.Open.AutoCancellationToken: a low-level Caravela aspect that adds cancellation tokens to your method declarations and your method calls.

  • Caravela.Open.Virtuosity: a low-level Caravela aspect that makes your methods virtual (a fork of Virtuosity.Fody).

  • Caravela.Open.DependencyEmbedder: a low-level Caravela aspect that embeds dependent assemblies into managed resources (a fork of Costura.Fody).

All examples are open source.

We would love your feedback!

If you have any feedback regarding Caravela, please open an issue, start a discussion, or contact us directly at

Debugging code with Caravela

By default, the debugger will show you your source code, not the transformed code. To see and step into the transformed code, see Debugging.

Writing your own aspects

Caravela.Framework: the simple and safe aspect framework

Caravela.Framework is an aspect-oriented framework that allows you to write code transformations and code generators in a simple and natural way, without working with compiler APIs.

Caravela.Framework is now in VERY EARLY PREVIEW. It is not considered to be complete except for the simplest use cases. Our ambition is to implement all features of PostSharp MSIL into Caravela.Framework.

Caravela.Framework.Sdk: the low-level extensibility API

Caravela.Framework.Sdk is the low-level API, which allows you to transform any Roslyn compilation in any way, without any guard or simplification.

Caravela.Framework.Sdk is considered to be almost final. We don't expect many changes.

How does PostSharp "Caravela" compare to Roslyn source generators?

Unlike Roslyn source generators, PostSharp "Caravela":

  • can replace or enhance hand-written code (Roslyn source generators are additive only: you just can add partial classes);
  • allows you to write aspects (or code transformations):
    • in your main project (instead of a separate project),
    • using the C# language, with Intellisense and code validation (instead of building a string);
  • is therefore a real and complete framework for aspect-oriented programming in C#, with the same level of functionality than what exists in other languages (such as AspectJ for Java).

How does PostSharp "Caravela" compare to PostSharp MSIL?

PostSharp "Caravela" was designed from scratch. It is based on best lessons learned from PostSharp MSIL during the last 15 years, and addresses the main obstacles that are now hindering PostSharp MSIL.

You will enjoy the following benefits with Caravela compared to PostSharp:

  • Faster builds: Caravela runs directly inside the compiler process (it is a fork of Roslyn), does not require an external process, and is therefore much faster;
  • More powerful transformations: The templating technology used by Caravela allows for more control over code than what was possible with PostSharp MSIL.
  • Better multi-platform support: Caravela does not load the whole project being built in the compiler process, therefore it avoids the cross-compilation issues that have plagued PostSharp for many years;
  • Better design-time experience: You will see introduced members and interfaces in Intellisence because Caravela will do that at design time and not at post-compilation time. No need for weird casts.
  • Better run-time performance: Because of code generation improvements, you can create aspects that execute much faster.
  • Better debugging experience: You can switch from source code view to transformed code view can debug the code exactly how it is executed.

Compatibility with PostSharp MSIL

How compatible do we intend to be with PostSharp MSIL? How much code will you need to rewrite?

It has been 12 years since the last major breaking change in PostSharp. Do you remember the .NET landscape in 2008? Clearly, we cannot build a new platform by keeping compatibility with designs that were optimal 12 years ago. However, we understand that PostSharp is used by thousands and we want to find a compromise between modernity and backward compatibility.

We have already taken the following compromise:

  • your aspect code (typically less than a dozen of classes) will need to be totally rewritten,
  • your business code should not be affected.


The foundation of PostSharp "Caravela" is the package Caravela.Compiler, a fork of Roslyn (the C# compiler) that adds to the compiler the ability to execute custom source code modifying extensions. When you build a project using Caravela, this fork of Roslyn is loaded instead of the Microsoft vanilla C# compiler.

The Caravela.Compiler package is not designed to be used or extended by end users.

Caravela.Framework is an add-in (the only one) to Caravela.Compiler. It contains the code transformation framework.

Caravela.Framework is designed to be hostable by Visual Studio and to integrate with design-time source generators, although this feature has not yet been implemented.