Broadening Pattern Matching

A quick update in the Dotty News department: the pre-SIP discussion has begun for Dotty’s name-based pattern matching.

I don’t have much to add to the links above, which are worth reading, but the tl;dr (as I understand it) is that Scala 2’s pattern-matching approach (that you write extractors that return specific types) is being replaced by a name-based approach that lets you return types that have specific names of methods. So instead of having to specifically return Option, you have to return a type that has get and isEmpty members.

In that sense, it’s similar to the way for comprehensions work: theoretically, you feed Monads into for comprehensions, but in reality you can give them anything that looks like a Monad — types with map, flatMap, foreach and/or withFilter methods, depending on what you do in your for.

It’s more general than the existing scheme, and should allow for lower-overhead extractors when that matters. Seems like a win to me, but if you have thoughts or opinions, I recommend checking out the discussion…