The classes serve to close some functions over variables for convenience; the attr_readers serve as destructuring functions for convenience; the += replaces a r

The classes serve to close some functions over variables for convenience; the attr_readers serve as destructuring functions for convenience; the += replaces a recursive function for convenience and familiarity. The function with the += doesn't mutate any value and it remains pure from all callers' perspectives. You're complaining about syntax, but this screencast is about semantics.