I suppose ruby is the example where you have map! and map. I don't know - the java stream API is clear enough IMO. The Java8 approach was to allow mutating func

I suppose ruby is the example where you have map! and map. I don't know - the java stream API is clear enough IMO. The Java8 approach was to allow mutating functions on collections and then have lazy-non mutative stream api. As a java8 dev, I don't think it's so hard to understand that map on a play promise is non mutative though - I'm not dropping requests for typesafe to change the api.