This behavior is underspecified but intended, though it might appear confusing. We plan to elaborate on the role of return type in macro signatures, but at the moment I feel like the flexibility is a good thing to have. Also at times the behavior is inconsistent, e.g. when the macro is caught in the middle … Read more
Just in case, here is what I meant by hiding ViewOf inside a type class (type classes is an alternative to match types). Sadly, in Scala 3 this is wordy. (version 1) import scala.annotation.experimental import scala.quoted.{Expr, Quotes, Type, quotes} // Library part trait View extends Selectable { def applyDynamic(key: String)(args: Any*): Any = { println(s”$key … Read more
Theoretical part This is an architectural peculiarity of scalac that started leaking into the public API once we exposed internal compiler data structures in compile-time / runtime reflection in 2.10. Very roughly speaking, scalac’s frontend consists of a parser and a typer, both of which work with trees and produce trees as their result. However … Read more
With new method Symbol.newClass (Scala 3.1.3) this becomes quite easy: import scala.annotation.experimental import scala.quoted.* object NewClass { inline def newClass[A]: A = ${newClassImpl[A]} @experimental def newClassImpl[A: Type](using Quotes): Expr[A] = { import quotes.reflect.* val name: String = TypeRepr.of[A].typeSymbol.name + “Impl” val parents = List(TypeTree.of[A]) def decls(cls: Symbol): List[Symbol] = List(Symbol.newMethod(cls, “func”, MethodType(List(“s”))(_ => List(TypeRepr.of[String]), _ … Read more
This is actually in my opinion an appropriate use case for 2.10 macros: you want access to information that you know the compiler has, but isn’t exposing, and macros give you a (reasonably) easy way to peek inside. See my answer here for a related (but now slightly out-of-date) example, or just use something like … Read more