Expansion of default parameters for overloaded methods

[Aonodensetsu]

As per the scala tour, multiple functions with default parameters would conflict and therefore are not supported. This is indeed correct in the example given, however it fails to capture more complex scenarios.

// proposal
def add(x: Int, y: Int = 1): Int = x + y
def add(x: String, y: String = "1"): String = x + y

add("1")

These two functions are not permitted per the current rules, however the compiler would be able to infer which to use based on the type of the first parameter.

---

This can already be faked by trait apply, but obviously is not a good practice.

trait IFun:
  def apply(y: Int = 1): Int
trait SFun:
  def apply(y: String = "1"): String

def add(x: Int): IFun =
  y => x + y
def add(x: String): SFun =
  y => x + y

add("1")()

I don't know how useful exactly this would be in practice for methods, but it would definitely find some use in constructors.

// proposal
class X(x: String, y: String = "1"):
  def this(x: Int, y: Int = 1) =
    this(x.toString, y.toString)

X(1)