sofoklis

val n = None                              //> n  : None.type = None
val s = Some(1)                           //> s  : Some[Int] = Some(1)

val o = Option(3)                         //> o  : Option[Int] = Some(3)
o match {
  case Some(x) => println("Count to :" + x)
  case None => println("Dont count")
}                                               //> Count to :3
  
val s2 = Some(null)                             //> s2  : Some[Null] = Some(null)

sofoklis

class ContravariantType[-T] {
  // some functions and fields 
}

sofoklis

val contravariantType1: ContravariantType[String] = new ContravariantType[String] // Allowed
val contravariantType2: ContravariantType[Any] = new ContravariantType[String] // Compile error
val contravariantType3: ContravariantType[String] = new ContravariantType[Any] // Allowed

sofoklis

val covariantType1: CovariantType[String] = new CovariantType[String] // Allowed
val covariantType2: CovariantType[Any] = new CovariantType[String] // Allowed
val covariantType3: CovariantType[String] = new CovariantType[Any] // Compile error

sofoklis

class CovariantType[+T] {
  // some functions and fields 
}

sofoklis

val string: Any = "sofoklis" // String is a proper subtype of any

val nonVariantType1: NonVariantType[String] = new NonVariantType[String] // Allowed
val nonVariantType2: NonVariantType[Any] = new NonVariantType[String] // Compile error
val nonVariantType3: NonVariantType[String] = new NonVariantType[Any] // Compile error

sofoklis

class NonVariantType[T]
{
  // some functions and fields 
}

sofoklis

package org.example
import scala.concurrent.{ Future, Promise, future, promise }
import scala.concurrent.ExecutionContext.Implicits.global

class FuturesAndPromises

object FuturesAndPromises {

  def main(args: Array[String]) {
    futureSample

sofoklis

(x ⇒ x match { case Some(v) ~ f ⇒ !f; case None ~ f ⇒ f })

sofoklis

opt("not") ~ b_factor