How to get the name of a nested object in Scala without its package name and without $?

Question

There is already In Scala, how do I get the *name* of an `object` (not an instance of a class)? but I have the following code:

package test

object A {
  object B {
    object C
  }
}

val tmp = A.B.C

I would like to get the string "A.B.C" from value tmp at runtime, so no package name and no $ since this is the same name used in pattern matching for the type.

I tried the following:

tmp.getClass.getSimpleName // leads to exception "Malformed class name"
tmp.getClass.getName // has package name and $ characters
tmp.getClass.getTypeName // the same
msg.getClass.getName.replace("$", ".") // we still have the package name

I want to get the exact same name as in the AST for pattern matching:

case A.B.C =>

Note that neither the package name nor the object names are fixed.

You cannot state that you want to «get the string "A.B.C"», and at the same time pattern match using it as it was a type («case A.B.C» - unquoted, so not a string). — Volty De Qua, Aug 15 '19 at 00:14

Alexey Romanov · Answer 1 · 2019-08-16T20:54:55.760

0

we still have the package name

So remove it:

val cls = tmp.getClass
cls.getName.stripPrefix(cls.getPackage.getName + ".").stripSuffix("$").replace("$", ".")

(the suffix is because it's an object)

edited Aug 16 '19 at 20:54

answered Aug 15 '19 at 02:36

Alexey Romanov

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This returns ".A.B.C.". You should strip the prefix and postfix dots. – SwiftMango Aug 15 '19 at 03:03

Volty De Qua · Answer 2 · 2019-08-15T11:21:01.847

package whatever.however 

import scala.util.matching.Regex

object O {
  object A {
    object B {
      object C
      object D
    }
  }

  def relativeType2String(a: Any): String = {
    s"^${ Regex.quote(this.getClass.getName)}(\\.|\\$$)?(.*?)(\\$$)?$$".r.replaceFirstIn(a.getClass.getName, "$2").replace('$', '.')
  }

  // println(typeStringRelativeToHere(tmp))
}


object Run extends App {
  val tmp = O.A.B.C
  println(O.relativeType2String(tmp))

  // or match on type  
  import O._
  def onType(t: Any) = t match {
    case A.B.C => println("it's A.B.C")
    case A.B.D => println("it's A.B.D")
  }
  val tmp2 = A.B.D
  onType(tmp)
  onType(tmp2)
}

outputs

[info] A.B.C                                                                                                                                                                                                                
[info] it's A.B.C                                                                                                                                                                                                           
[info] it's A.B.D

~
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How to get the name of a nested object in Scala without its package name and without $?

2 Answers2