private keyword has different meaning on class definition-CodePudding

I think I had a good understanding of Scala till I find myself in this simple scenario

sealed abstract case class Name private(name: String)

object Name {
    def make(name: String): Option[Name] =
      if (name.nonEmpty) Some(new Name(name) {}) else None
  }

my question is about the private modifier for the class. If I use it like this, everything works, but if I move the private keyword at the start, something like

private sealed abstract case class Name(name: String) it doesn't compile becuase gives me the following error

private class Name escapes its defining scope as part of type Option[example.package.Name]

where example.package is the package object I'm working in.

I think I need some clarification because I'm not sure what's happening here

CodePudding user response：

sealed abstract case class Name(name: String)

Name effectively denotes both

the name of the class
the default constructor for that class

sealed abstract case class Name private(name: String)

declares that the class is public, but the constructor is private (i.e. can only be called from within that class or its companion object).

private sealed abstract case class Name(name: String)

declares that the class is private (which implies that the constructor is also private).

CodePudding user response：

This code compiles with no error:

 private sealed abstract case class Name(name: String)

The problem is that you are then returning a value that contains a public value of this class, so the definition is leaking out and it isn't really private. You need to make sure that all references to Name are also private.

The first syntax marks the constructor as private;

sealed abstract case class Name private(name: String)

This means that the constructor can only be called from inside the Name companion object. So this is not allowed

val name = new Name("name") // constructor Name in class Name cannot be accessed