Feature #13224
Updated by nobu (Nobuyoshi Nakada) about 7 years ago
Currently, attempting to modify a frozen object leads to a `RuntimeError` exception. Unfortunately, this means it is not easy to differentiate exceptions raised from attempting to modify frozen objects from generic exceptions such as calling `Kernel#raise` with no exception class. The attached patch adds `FrozenError` as a subclass of `RuntimeError`, and uses `FrozenError` instead of `RuntimeError` for exceptions raised when there is an attempt to modify a frozen object. It should be backwards compatible in the sense that: ~~~ruby ~~~ begin "a".freeze << b b' rescue RuntimeError end ~~~ Will still function as before. More people in the ruby community are starting to use frozen objects for the benefits of immutability (thread-safety, cache-ability, referential transparency), and having an exception class dedicated to misuse of frozen objects will make it easier to handle those exceptions. The attached patch is a little long, mostly because ruby's test suite is currently brittle in regards to handling exception classes. For example, `assert_raise(RuntimeError)` needs to be changed to `assert_raise(FrozenError)`, because `assert_raise` uses `instance_of?` instead of `kind_of?` if given an exception class and not a module. Both RSpec and recent versions of Minitest should automatically handle this type of change without code modifications.