Givens in Scala 3 as behaviours injected into functions
Note
What is the use case of givens in Scala 3? They are a replacement for implicits, avoiding to explicitly have to pass instances used at call site. Given is well named - it is considered a "given" to the function. We don't instantiate it as we do with implicits, but rather automatically creates instances to be injected in the function at call site.
An example of a given instance that defines an ordering behaviour for a custom type Person:
given personOrdering as Ordering[Person] {
override def compare(x: Person, y: Person): Int =
x.surname.compareTo(y.surname)
}
And then in the function to use it:
def listPeople(people: List[Person])(using ordering: Ordering[Person]) = ???
This way we don't need to explicitly pass the ordering argument. We are using the ordering behaviour we have previously defined for the Person type. This encodes the concept of type classes, e.g. behaviours for types.
