abstract class A {
  val message: String
}
class B extends A {
  val message = "I'm an instance of class B"
}
trait C extends A {
  def loudMessage = message.toUpperCase()
}
class D extends B with C

val d = new D
println(d.message)  // I'm an instance of class B
println(d.loudMessage)  // I'M AN INSTANCE OF CLASS B

abstract class A:
  val message: String
class B extends A:
  val message = "I'm an instance of class B"
trait C extends A:
  def loudMessage = message.toUpperCase()
class D extends B, C

val d = D()
println(d.message)  // I'm an instance of class B
println(d.loudMessage)  // I'M AN INSTANCE OF CLASS B

Class D has a superclass(부모클래스) B and a mixin C. Classes can only have one superclass but many mixins (using the keywords extends and with respectively). The mixins and the superclass may have the same supertype.

→ 수퍼클래스와 믹신 둘다 A라는 부모클래스를 동일하게 가질 수 있다는 것

→ 클래스를 합성하는 방법

mixins은 트레이트들이다. 즉 클래스를 합성하는데 쓰게 된다.

클래스 D는 B를 상속받으면서 C의 기능또한 활용가능하다.

abstract class AbsIterator {
  type T
  def hasNext: Boolean
  def next(): T
}

abstract class AbsIterator:
  type T
  def hasNext: Boolean
  def next(): T

Next, we’ll implement a concrete class (all abstract members T , hasNext , and next  have implementations):

class StringIterator(s: String) extends AbsIterator {
  type T = Char
  private var i = 0
  def hasNext = i < s.length
  def next() = {
    val ch = s charAt i
    i += 1
    ch
  }
}

class StringIterator(s: String) extends AbsIterator:
  type T = Char
  private var i = 0
  def hasNext = i < s.length
  def next() =
    val ch = s charAt i
    i += 1
    ch

위에서 만든 absiterator를 상속

trait RichIterator extends AbsIterator:
  def foreach(f: T => Unit): Unit = while hasNext do f(next())

→ 반환값없이 어떠한 연산을 하겠다.

class RichStringIter extends StringIterator("Scala") with RichIterator
val richStringIter = new RichStringIter
richStringIter.foreach(println)

class RichStringIter extends StringIterator("Scala"), RichIterator
val richStringIter = RichStringIter()
richStringIter.foreach(println)

→ with로 트레이트를 상속받아서 그 내의 함수를 사용가능