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Description
sample project : https://github.com/seraphr/scala-macro-strange-behavior
./sbt uses/clean uses/runmacro
when this macro is defined
import scala.language.experimental.macros
import scala.reflect.macros.whitebox.Context
object Members {
def apply[A]: List[String] = macro macroImpl[A]
def macroImpl[A: c.WeakTypeTag](c: Context): c.Tree = {
import c.universe._
val tType = weakTypeOf[A]
val tMembers = tType.members.map(_.name.toString).toList
q"${tMembers}"
}
}
h3. case 1 - same file
run this code
case class Foo(a: Int, b: Long = 20, c: String = "aaa")
object Main extends App {
val tFooMembers = Members[Foo]
val tBarMembers = Members[Bar]
val tFooCompanionMembers = Members[Foo.type]
val tBarCompanionMembers = Members[Bar.type]
println(s"Foo diff Bar = ${tFooMembers diff tBarMembers}")
println(s"Bar diff Foo = ${tBarMembers diff tFooMembers}")
println(s"FooCompanion diff BarCompanion = ${tFooCompanionMembers diff tBarCompanionMembers}")
println(s"BarCompanion diff FooCompanion = ${tBarCompanionMembers diff tFooCompanionMembers}")
}
case class Bar(a: Int, b: Long = 20, c: String = "aaa")Foo and Bar have same members, but output is
Foo diff Bar = List(copy$default$3, copy$default$2, copy$default$1)
Bar diff Foo = List()
FooCompanion diff BarCompanion = List($lessinit$greater$default$3, $lessinit$greater$default$2)
BarCompanion diff FooCompanion = List()case 2 - different file
- Baz.scala
case class Baz(a: Int, b: Long = 20, c: String = "aaa")- Qux.scala
case class Qux(a: Int, b: Long = 20, c: String = "aaa")- Main.scala
object Main extends App {
val tBazMembers = Members[Baz]
val tQuxMembers = Members[Qux]
val tBazCompanionMembers = Members[Baz.type]
val tQuxCompanionMembers = Members[Qux.type]
println(s"Baz diff Qux = ${tBazMembers diff tQuxMembers}")
println(s"Qux diff Baz = ${tQuxMembers diff tBazMembers}")
println(s"BazCompanion diff QuxCompanion = ${tBazCompanionMembers diff tQuxCompanionMembers}")
println(s"QuxCompanion diff BazCompanion = ${tQuxCompanionMembers diff tBazCompanionMembers}")
}Baz and Qux have same members, but output is
Baz diff Qux = List(copy$default$3, copy$default$2, copy$default$1)
Qux diff Baz = List()
BazCompanion diff QuxCompanion = List(readResolve, apply$default$3, apply$default$2, $lessinit$greater$default$3, $lessinit$greater$default$2)
QuxCompanion diff BazCompanion = List()
this behavior depends on filename.