Question

Why is the scala list implementation named :: and not a class name? Is there some special meaning behind that?

Answer 1

This is to work with pattern matching. You have something called an Infix Operator Patterns where pattern p op q is equivalent to the constructor or extractor pattern op(p, q).

So the case class :: defines the constructor ::(head, tail). That allows you to match like this:

list match {
  case ::(head, tail) =>
}

But with the infix operator pattern, you can write the more familiar syntax:

list match {
  case head :: tail =>
}

Note that a stackoverflow search on “[scala] infix operator pattern” returns similar questions and additional use cases of the pattern.