Cannot infer type of tupled arguments

[giacomocavalieri]

Compiler version

Scala 3.0.2 (Scastie)

Minimized code

type ~>[Args <: Tuple, Return] = Args match {
  case (arg1, arg2) => ((arg1, arg2) => Return)
}

trait Builder[Args <: NonEmptyTuple] {
  def apply(f: Args ~> String): String
}

class BuilderImpl[Args <: NonEmptyTuple] extends Builder[Args] {
  override def apply(f: Args ~> String): String = ???
}

val builder = BuilderImpl[Int *: String *: EmptyTuple]()
// builder { (i: Int, s: String) => "test" } // This line compiles
builder { (i, s) => "test" } // Does not compile

Output

Missing parameter type I could not infer the type of the parameter i.
Missing parameter type I could not infer the type of the parameter s.

Expectation

No compiler error; I would expect the compiler to be able to infer the type of the function's arguments without annotations.

[nicolasstucki]

Side note

@giacomocavalieri it seems that to use this you would also need TupledFunction. How did you implement the BuilderImpl.apply?

[giacomocavalieri]

Thanks for the answer! I still haven't tried to implement the apply method since I first wanted to understand why the compiler reported that error