In Scala, what does “extends (A => B)” on a case class mean?

Question

In researching how to do Memoization in Scala, I\'ve found some code I didn\'t grok. I\'ve tried to look this particular \"thing\" up, but don\'t know by what to call it; i.

Answer 1

A => B is short for Function1[A, B], so your Memo extends a function from A to B, most prominently defined through method apply(x: A): B which must be defined.

Because of the "infix" notation, you need to put parentheses around the type, i.e. (A => B). You could also write

case class Memo[A, B](f: A => B) extends Function1[A, B] ...

or

case class Memo[A, B](f: Function1[A, B]) extends Function1[A, B] ...