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

I am the original author of doing memoization this way. You can see some sample usages in that same file. It also works really well when you want to memoize on multiple arguments too because of the way Scala unrolls tuples:

    /**
     * @return memoized function to calculate C(n,r) 
     * see http://mathworld.wolfram.com/BinomialCoefficient.html
     */
     val c: Memo[(Int, Int), BigInt] = Memo {
        case (_, 0) => 1
        case (n, r) if r > n/2 => c(n, n-r)
        case (n, r) => c(n-1, r-1) + c(n-1, r)
     }
     // note how I can invoke a memoized function on multiple args too
     val x = c(10, 3)