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scalascala-macrosscala-macro-paradise

Macro annotation with default arguments

Getting Parameters from Scala Macro Annotation explains how to get parameters from a macro annotation. However, if I have several parameters with default values: 

class Foo(b: Boolean = false, i: Int = 0) extends StaticAnnotation { ... }

I need to write (based on the answer to that question)

val (b, i) = c.prefix.tree match {
  case q"new Foo(..$args)" => ???
}

The logic in ??? seems to become very nasty: I need to handle both positional and named parameters, no simple access to the default values, etc. Is there a way to simplify it?

Solution

  • Well, this is a limited solution, but

    // same constructor parameters and defaults as Foo
class FooArgs(b: Boolean = false, i: Int = 0)

val args = c.prefix.tree match {
  case q"new Foo(...$args)" => c.eval(c.Expr[FooArgs](q"new some_package.FooArgs(...$args)"))
}