Function and PartialFunction Scala classes

Function.scala

// func1 and func2 are synonyms
val func1 = (x: String) => "hello %s".format(x)
func1("world")
func1.apply("world")

val func2 = new Function1[String, String] {
  def apply(x: String) = "hello %s".format(x)
}
func2("world")
func2.apply("world")

/**************************************************/

// pfunc3 and pfunc4 are synonyms
val pfunc3 = new PartialFunction[Int, Int] {
  def apply(d: Int) = 42 / d
  def isDefinedAt(d: Int) = d != 0
}
pfunc3.isDefinedAt(41)
func3(42)

val pfunc4: PartialFunction[Int, Int] = { 
  case d: Int if d != 0 ⇒ 42 / d 
}
pfunc4.isDefinedAt(41)
func4(42)

http://blog.bruchez.name/2011/10/scala-partial-functions-without-phd.html
https://blog.matthewrathbone.com/2017/03/06/scala-object-apply-functions.html