Scala Programming Projects

cats.Semigroup

In the type class introduction, we defined a Combine type class. It turns out that this type class is already defined in the Cats library. Its name is Semigroup; this name comes from the mathematical representation of this algebraic structure.

Open it in IntelliJ to see how it is defined:

/**
 * A semigroup is any set `A` with an associative operation (`combine`).
 */
trait Semigroup[@sp(Int, Long, Float, Double) A] extends Any with Serializable {
  /**
   * Associative operation taking which combines two values.
   */
  def combine(x: A, y: A): A
(...)
}

The @sp annotation is an optimization to avoid the boxing/unboxing of primitive types. Apart from that, the definition of Semigroup is the same as our Combine type class.