Why doesn't Option have a fold method?

Question

I wonder why scala.Option doesn\'t have a method fold like this defined:

fold(ifSome: A => B , ifNone: => B)

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Answer 1

As mentioned by Debilski, you can use Scalaz's OptionW.cata or fold. As Jason commented, named parameters make this look nice:

opt.fold { ifSome = _ + 1, ifNone = 0 }

Now, if the value you want in the None case is mzero for some Monoid[M] and you have a function f: A => M for the Some case, you can do this:

opt foldMap f

So,

opt map (_ + 1) getOrElse 0

becomes

opt foldMap (_ + 1)

Personally, I think Option should have an apply method which would be the catamorphism. That way you could just do this:

opt { _ + 1, 0 }

or

opt { some = _ + 1, none = 0 }

In fact, this would be nice to have for all algebraic data structures.