A Stack[T] method needs to transform values into a new type U. Which declaration is valid…

A Stack[T] method needs to transform values into a new type U. Which declaration is valid Go?

1. A standalone function MapStack[T, U any](Stack[T], func(T) U) Stack[U]
2. A method func (s Stack[T]) Map[U any](func(T) U) Stack[U]
3. A method that declares U after its return type