After my time with Scala, I think that if I need a heavy type system, I'd look to Haskell. And there are certainly classes of problems that I would choose a type system, but the general case isn't nearly as strong as I though it was before seeing them used in anger.

So, in the following, I'm not ranting at you, but I am saying I see lots of arguments for types that jump to QED without nearly enough evidence, with the "everybody knows" kinda explanation. And you happen to have put a handy list right in front of me when I had time to respond.

> ... difficulties with refactoring, runtime errors, needing lots of test coverage and not scaling well to large teams and codebases.

I was really impressed with Scala when learning or toy projects, but every time I saw it in production it was pretty horrid. Small, technical refactoring was taken care of by the IDE, but large scale refactoring takes the same amount of thought as before, but now there's 10x as much code to understand first.

There were less runtime errors, but not much less, and I saw a lot of code that didn't error, but didn't get done what it needed to.

When it comes to scaling to large teams, I saw lots of "The compiler says it's ok, and the tests pass, so commit!" where the code didn't make sense! The old thing about write code for programmers to understand first, and the machine to understand second...

Outside of certain specific situations, I just haven't seen the benefits outweigh the increased code weight and slower time to market.