scala-macros – Tarik Billa

Scala Macros: Making a Map out of fields of a class in Scala

December 4, 2023 by Tarik

Note that this can be done much more elegantly without the toString / c.parse business: import scala.language.experimental.macros abstract class Model { def toMap[T]: Map[String, Any] = macro Macros.toMap_impl[T] } object Macros { import scala.reflect.macros.Context def toMap_impl[T: c.WeakTypeTag](c: Context) = { import c.universe._ val mapApply = Select(reify(Map).tree, newTermName(“apply”)) val pairs = weakTypeOf[T].declarations.collect { case m: MethodSymbol … Read more

Scala macros and the JVM’s method size limit

September 14, 2023 by Tarik

Imo putting data into .class isn’t really a good idea. They are parsed as well, they’re just binary. But storing them in JVM may have negative impact on performance of the garbagge collector and JIT compiler. In your situation, I would pre-compile the XML into a binary file of proper format and parse that. Elligible … Read more

How to make IntelliJ IDEA recognise code created by macros?

August 18, 2023 by Tarik

With the latest Scala plugin build, there is an API which can be used to write your own plugin to support your macros: http://blog.jetbrains.com/scala/2015/10/14/intellij-api-to-build-scala-macros-support/ Now, everyone can use this API to make their macros more friendly to their favorite IDE. To do that, you have to implement SyntheticMembersInjector, and register it in the plugin.xml file: … Read more

Where can I learn about constructing AST’s for Scala macros?

August 8, 2023 by Tarik

There isn’t a lot of documentation for the internals of the compiler available, but the things that are available should be enough to get started. Mirko Stocker, has written his Master Thesis about Scala Refactoring. In Appendix D (p. 95) he describes the architecture of the AST. It includes also a graphical overview: Another way … Read more

Iteration over a sealed trait in Scala?

July 30, 2023 by Tarik

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 See my answer here for a related (but now slightly out-of-date) example, or just use something like … Read more

Static return type of Scala macros

July 27, 2023 by Tarik

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

Documenting Scala 2.10 macros [closed]

February 22, 2023 by Tarik

I think the best way to document these is with example code, as Miles has been doing in his experimental macro based branch of shapeless.

Getting a structural type with an anonymous class’s methods from a macro

October 22, 2022 by Tarik

This question is answered in duplicate by Travis here. There are links to the issue in the tracker and to Eugene’s discussion (in the comments and mailing list). In the famous “Skylla and Charybdis” section of the type checker, our hero decides what shall escape dark anonymity and see the light as a member of … Read more

How to use Shapeless in a Quasiquote?

October 3, 2022 by Tarik

This is my working solution using old-style macro annotations. import scala.language.experimental.macros import scala.reflect.macros.blackbox.Context import scala.annotation.StaticAnnotation class fieldable extends StaticAnnotation { def macroTransform(annottees: Any*): Any = macro fieldableMacro.impl } object fieldableMacro { def impl(c: Context)(annottees: c.Expr[Any]*): c.Tree = { import c.universe._ annottees.map(_.tree) match { case (param @ q”case class $className(..$fields)”) :: Nil => { val implicits … Read more