So after working at Google for 6 years (and doing Java and other things prior) I went to Facebook and programmed in Hack for 4 years. Hack is actually a really

So after working at Google for 6 years (and doing Java and other things prior) I went to Facebook and programmed in Hack for 4 years. Hack is actually a really interesting and convenient language in many ways. One way I really appreciated is how nullability is built into the type system. Having to deal with nullability in Java is actually way more of a chore than any of the verbosity that people normally complain about (eg boilerplate around anonymous classes). The story I like to tell about how people abuse Java is this: @nullable Optional<Boolean> I don't know if this is still the case but you could literally find many instances of that in Google3 (and not all of them were the product of an auto-generated tool). I mean it's a super-large code base. There was a cleanup at one point for the (many) instances of 1204 in the code base. The way I like to describe this is "for when 3 values for your boolean just aren't enough" (since you obviously now have 4 states: 1) null 2) Not set 3) Set, true 4) Set, false). I have a few rules that have held up v ery well over the years including: 1. If you don't do arithmetic on it and it's not an ID of some kind, it's almost certainly not a number (eg people who store SSNs as INT fields); and 2. It's almost never a boolean. You're almost always better off replacing any boolean with an enum. Not only is this typesafe but if done right adding an enum value will cause compiler errors because you've been exhausitve with switches without a default case.