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
Scala 2 version of this answer is here: How can I run generated code during script runtime? In Scala 3: For example you can use Li Haoyi‘s Ammonite ammonite.Main(verboseOutput = false).runCode(“””println(“Hello, World!”)”””) // Hello, World! build.sbt scalaVersion := “3.1.3” libraryDependencies += “com.lihaoyi” % “ammonite” % “2.5.4-22-4a9e6989” cross CrossVersion.full excludeDependencies ++= Seq( ExclusionRule(“com.lihaoyi”, “sourcecode_2.13”), ExclusionRule(“com.lihaoyi”, “fansi_2.13”), … Read more
You don’t need any 3rd party library to do this: sealed trait MyTrait case object SubClass1 extends MyTrait case object SubClass2 extends MyTrait import scala.reflect.runtime.{universe => ru} val tpe = ru.typeOf[MyTrait] val clazz = tpe.typeSymbol.asClass // if you want to ensure the type is a sealed trait, // then you can use clazz.isSealed and clazz.isTrait … Read more
First for some shameless self-promotion: Eugene Burmako and I are giving a talk on type providers, a closely related topic, at Scalar 2014 tomorrow, and I encourage you to take a look at the example project we put together for the talk if you’re interested in this kind of thing. While type macros are no … Read more
Here’s an implementation that’s also a little more generic: import scala.language.experimental.macros object WithIdExample { import scala.reflect.macros.Context def withId[T, I](entity: T, id: I): T = macro withIdImpl[T, I] def withIdImpl[T: c.WeakTypeTag, I: c.WeakTypeTag](c: Context)( entity: c.Expr[T], id: c.Expr[I] ): c.Expr[T] = { import c.universe._ val tree = reify(entity.splice).tree val copy = entity.actualType.member(newTermName(“copy”)) val params = copy … Read more
To the best of my knowledge, there’s no standard way to go from a symbol to a defining tree. Your best bet would probably be to iterate through c.enclosingRun.units, recursing into each of the unit.body trees as you go. If you see a DefDef, which has a symbol equal to your symbol, then you’ve reached … Read more
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
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
Using standard type class derivation in Dotty import scala.deriving.Mirror case class ParseError(str: String, msg: String) trait Decoder[T]{ def decode(str:String): Either[ParseError, T] } object Decoder { given Decoder[String] with { override def decode(str: String): Either[ParseError, String] = Right(str) } given Decoder[Int] with { override def decode(str: String): Either[ParseError, Int] = str.toIntOption.toRight(ParseError(str, “value is not valid Int”)) … 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