CODEWITHSUNDEEP
scalascalameta
LoranceChen
LoranceChen

Reputation: 2574

How to get a method return type with scala meta annotation?

I want do a Log annotation use scala meta.Usage simple as: 

@Log
def f1(a: Int) {
    Future(a + 1) //result is a Future
}

// after parsed ====>
def f1(a: Int) {
    Future(a + 1).map{x => 
        println(x)
        x
    }
}

How can I check if f1 is a Future[ _ ] type? Thanks
Besides, I don't want use reflection(performance cost) in Log annotation and I think method result type can be decided at compile time.

Upvotes: 2

Views: 359

Answers (1)

Ólafur Páll Geirsson
Ólafur Páll Geirsson

Reputation: 421

This is not possible with scalameta macro annotations. The macro annotations are syntactic so they don't have access to semantic information such as types of trees.

PS. I am not sure if a macro annotation is suitable for this use-case, you could write out the log statement explicitly with something like this

def log[T](x: T): T = { println(x); x }
Future(1).map(log)

or even more concisely with an extension method

implicit class XtensionFuture[T](future: Future[T]) {
  def logged: Future[T] = future.map(log)
}
Future(1).logged

Macros should ideally be used as a last resort, not for convenience only.

Upvotes: 1

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