CODEWITHSUNDEEP
scalascala-macros
Christian Schlichtherle
Christian Schlichtherle

Reputation: 3155

How to programmatically generate an abstract Scala class extending an annotated trait?

Given an annotated trait, how should I go about generating an abstract class which implements the trait?

So, given the following user trait...

@Neuron
trait SomeTrait {
  // ...
}

... in my library I want to insert something like the following next to it:

abstract class SomeTraitImpl extends SomeTrait

Note that I know nothing about the given trait except it's annotated with @Neuron.

I've tried to do this with ASM, implementing the concept explained in the answer to the question Using Scala traits with implemented methods in Java, but this concept scratches only the surface of what the Scala compiler emits as byte code. Even if I succeeded to master all possible combinations of var, val, lazy val, abstract override etc the odds are high that it will break with the next release of the Scala compiler.

So it looks like I should write a compile time macro instead. However, I am scratching my head over the documentation for Scala macros, so I wonder if anyone could draft something which gets me started? Any hint is appreciated, please!

Upvotes: 1

Views: 250

Answers (1)

Christian Schlichtherle
Christian Schlichtherle

Reputation: 3155

The correct approach to do this is to make @Neuron a macro annotation (using the Macro Paradise compiler plugin) and implement the macro to do the code transformation. The resulting code is now part of Neuron DI, a framework for dependency injection which I wrote.

Upvotes: 0

Related Questions