Type Classes (Cats-style)

Code

// Define
trait Semigroup[A] {
  def combine(x: A, y: A): A
}

// Instances
implicit val intSum: Semigroup[Int] = (x, y) => x + y
implicit val strConcat: Semigroup[String] = (x, y) => x + y

// Generic function
def combineAll[A](xs: List[A])(implicit s: Semigroup[A]): A =
  xs.reduce(s.combine)

combineAll(List(1, 2, 3))           // 6
combineAll(List("a", "b", "c"))     // "abc"

// Cats provides Monoid, Functor, Monad, etc. the same way

Explanation

Type classes let you add behavior to types retroactively without modifying them. Define the trait, provide instances, and write generic functions. Cats is the mainstream library. This is more flexible than OOP inheritance and powers Haskell-style polymorphism in Scala.

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