Source Generators
Source Generators is a feature that allows us to generate new code, based on existing (written by us) code (and other files). The generation happens at compile time.
Generation can happen not only based on source code, but also based on other
kinds of files, like .txt files for example. E.g., a txt file containing a
list of words could be there, and some enum could be generated based on that.
It’s often needed to extend some existing class via source generation. In order
for a class to be extensible this way, it has to be partial. Since source
generator can only add new code, and cannot modify existing source, this is the
only way to extend existing classes.
Source Generators run during compilation. When working on a project in an IDE, projects could be often built, and sevice generators could be invoked often. Performance could become an issue (of developer workflow only, since runtime will not be hit by that!)
Incremental Generators
Starting with .NET 6, source generator classes have to:
- implement the IIncrementalGeneretor interface
- have the
[Generator]attribute
Incremental Generator is a pipeline of operations that lead to new source code generation. An important part of it is memoization. Stages of the pipeline utilize caching. This is due to the feet that every code change triggers compilation in IDE. To not kill performance, incremental generator will only run these stages of the pipeline that will produce different results than before.
Interesting Use Cases
Performant Logging
The Microsoft.Extensions.Logging package from Microsoft has a built-in support
for source-generated
logs.
Faster Enum to String
Andrew Lock has created a
NetEscapades.EnumGenerators
package, that will auto-generate (among other things) ToStringFast() methods
for each enum marked with [EnumExtensions] attribute. It is much faster than
reflection-based ToString().
Many other useful generators are listed here.