Scala companion class warning

Question

I am new to Scala programming, can someone explain me below warning reason?

I trie

Answer 1

Companion class and its object must be defined in the same file.

so you can write your class and object in a file and then using :paste in REPL you can run your code. no warning will appear.

scala> :paste
// Entering paste mode (ctrl-D to finish)

class Student(sid: Int, sname: String) {
    val id = sid
    val name = sname

    override def toString() = this.id + "," + this.name
  }

  object Student {
    def displayDetails(st: Student) = {
      println("Student Details : " + st.id + "," + st.name)
    }
  }


// Exiting paste mode, now interpreting.

defined class Student
defined object Student