Can I override a scala class method with a method from a trait?

Question

class PasswordCaseClass(val password:String)
trait PasswordTrait { self:PasswordCaseClass =>
    override def password = "blue"
}

val o = new PasswordCaseClass("flowers") with PasswordTrait

Is it possible to override PasswordCaseClass's password with what is provided in PasswordTrait? Right now, I receive this error:

e.scala:6: error: overriding value password in class PasswordCase
Class of type String;
 method password in trait PasswordTrait of type => java.lang.String needs to be a stable,
immutable value
val o = new PasswordCaseClass("flowers") with PasswordTrait
            ^
one error found

I would like to be able to have something like this:

class User(val password:String) {
}

trait EncryptedPassword { u:User =>
  def password = SomeCriptographyLibrary.encrypt(u.password)
}

val u = new User("random_password") with EncryptedPassword
println(u.password) // see the encrypted version here

Answer 1

You can override a def with a val, but you can't do it the other way around. A val implies a guarantee -- that it's value is stable and immutable -- that a def does not.