Intellij worksheet and classes defined in it

Question

I'm following along the Coursera course on functional programming in Scala and came along a weird behavior of the worksheet repl.

In the course a worksheet with the following code should give the following results on the right:

object rationals {
val x = new Rational(1, 2)              > x : Rational = Rational@<hash_code>
   x.numer                              > res0: Int = 1
   y. denom                             > res1: Int = 2
}

class Rational(x: Int, y: Int) {
   def numer = x
   def denom = y
}

What I get is

object rationals {                      > defined module rationals
val x = new Rational(1, 2)              
   x.numer                              
   y. denom                             
}

class Rational(x: Int, y: Int) {        > defined class Rational
   def numer = x
   def denom = y
}

Only after moving the class into the object I got the same result as in the code.

• Is this caused by Intellij, or have there been changes in Scala?
• Are there other ways around this?

Answer 1

In the IntelliJ IDEA scala worksheet handles values inside the objects differently than Eclipse/Scala IDE.

Values inside objects are not evaluated in linear sequence mode, instead they are treated as normal scala object. You barely see information about it until explicit use.

To actually see your vals and expressions simply define or evaluate them outside any object\class

This behaviour could be a saviour in some cases. Suppose you have that definitions.

  val primes = 2l #:: Stream.from(3, 2).map(_.toLong).filter(isPrime)

  val isPrime: Long => Boolean = 
    n => primes.takeWhile(p => p * p <= n).forall(n % _ != 0)

Note that isPrime could be a simple def, but we choose to define it as val for some reason.

Such code is nice and working in any normal scala code, but will fail in the worksheet, because vals definitions are cross-referencing.

But it you wrap such lines inside some object like

object Primes {
  val primes = 2l #:: Stream.from(3, 2).map(_.toLong).filter(isPrime)

  val isPrime: Long => Boolean =
    n => primes.takeWhile(p => p * p <= n).forall(n % _ != 0)
}

It will be evaluated with no problem