scala: how to define a value class

Question

Quick question regrading how to define a value class in scala

Here is typical example:

class Wrapper(val underlying: Int) extends AnyVal

I am getting next error:

/usr/home/User/scala2/scala_lerning/src3/val.scala:1: error: value class may not be a member of another class
class Wrapper(val underlying: Int) extends AnyVal
      ^
one error found

Could anyone help with this?

Thanks

The error message seems pretty explicit, a value class cannot be an inner class. — Marth, Feb 18 '16 at 09:57
Sorry, still open question for me. I am compiling this from command promt like: scala value.scala . Should I apply any class modifier in example above? — Pavel, Feb 18 '16 at 10:10
Seems to be related to how the `scala` command loads files. Compiling with `scalac` works fine, same with simply typing the line in the REPL or using `:load` within it. — Marth, Feb 18 '16 at 10:45

score 1 · Accepted Answer · answered Feb 18 '16 at 10:31

1

It seems you're doing

class Foo {
  class Wrapper(val underlying: Int) extends AnyVal
}

which you can't. You have to do

class Foo {
}
class Wrapper(val underlying: Int) extends AnyVal

answered Feb 18 '16 at 10:31

Reactormonk

21,472
14
74
123

1

I am getting the same error when I am putting your code in a single file and trying to compile: scala file.scala. – Pavel Feb 18 '16 at 10:36
Here is also example from scala documentation. It also fails: trait Printable extends Any { def print(): Unit = println(this) } class Wrapper(val underlying: Int) extends AnyVal with Printable val w = new Wrapper(3) w.print() // actually requires instantiating a Wrapper instance – Pavel Feb 18 '16 at 10:41
3

That's because you're invoking `scala file.scala` instead of `scalac file.scala`. Apparently `scala` wraps everything into a toplevel class to enable scripting. – Reactormonk Feb 18 '16 at 10:43

scala: how to define a value class

1 Answers1

Linked