Implicits (Given/Using in Scala 3)

Code

// Type class definition
trait Show[A] {
  def show(a: A): String
}

// Instance
implicit val showInt: Show[Int] = (a: Int) => a.toString

// Usage (implicit parameter)
def printIt[A](a: A)(implicit s: Show[A]): Unit =
  println(s.show(a))

printIt(42)  // "42" — compiler finds showInt

// Scala 3 syntax:
// given Show[Int] with { def show(a: Int) = a.toString }
// def printIt[A](a: A)(using s: Show[A]): Unit = ...

Explanation

Implicits (renamed to given/using in Scala 3) enable type classes, context passing, and extension methods. The compiler searches for matching instances in scope. They power libraries like Cats and Shapeless. Use them sparingly to avoid implicit ambiguity.

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