This is a great write up and I think the proposal to make rbs-inline type comments avaible at runtime is an execellent solution.

I can definitely see the value runtime type checking in addition to static analysis. For my own work I've done this either using pattern matching:

  class User
    def initialize(name:, age:)
      String => name
      Integer => age
      @name = name
      @age = age
    end
  end

but the error messages aren't great IMHO. It's pretty easy though knock up a little type checker in a very small module and prepend it. I have support for union types and typed arrays in mine.

I actually wasn't aware of the improvements they've made over the years to Sorbet. It think that's probably what I'll migrate to now.