Ending the confusion of private case class constructor in Scala 2.13 or 2.14

Design
11

It works, you need to instantiate an abstract subclass. Constructor is hidden, no default apply, no copy. Pattern matching works.

sealed abstract case class Foo private (s: String, n: Int)
object Foo {
  def apply(s: String): Foo =
    new Foo(s, s.length) {}
}
 
Foo("x", 42)     // nope
new Foo("x", 42) // nope

val a = Foo("x") 
// a: Foo = Foo("x", 1)

a.copy(n = 42)   // nope

val Foo(s, n) = a 
// s: String = "x"
// n: Int = 1
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