Errors: raise & rescue

raise — throwing on purpose

raise is Ruby's version of Swift's throw or Python's raise — you already know the shape. Give it an error class and a message:

raise ArgumentError, "minutes must be positive"

ArgumentError is one of many built-in error classes (TypeError, ZeroDivisionError, NoMethodError, and more) — pick the one that best describes what went wrong. Unhandled, raise crashes the program with that message and a backtrace, same as an uncaught exception in any language you know.