Feature #13224: Add FrozenError as a subclass of RuntimeError

• Status: Closed
• Assignee: -
• Target version: 2.5

[jeremyevans0 (Jeremy Evans)]

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:

begin
  "a".freeze << 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.

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[matz (Yukihiro Matsumoto)]

OK, accepted.

Matz.

[jeremyevans0 (Jeremy Evans)]

• File 0001-Add-FrozenError-as-a-subclass-of-RuntimeError.patch 0001-Add-FrozenError-as-a-subclass-of-RuntimeError.patch added

Matz accepted this feature about 6 months ago, but it didn't make it into 2.5.0-preview1. Attached is an updated patch that applies to current trunk.

[nobu (Nobuyoshi Nakada)]

Out of topic, Kernel.raise in examples should be Kernel#raise, I think.

[jeremyevans0 (Jeremy Evans)]

• File 0001-Add-FrozenError-as-a-subclass-of-RuntimeError.patch 0001-Add-FrozenError-as-a-subclass-of-RuntimeError.patch added
• Target version set to 2.5

There's less than a month until the release of 2.5.0, and this hasn't been merged yet. I've rebased the patch to apply to current trunk and made sure the tests pass. Since this feature was already accepted back in April, I'm assigning 2.5 as the target version.

[jeremyevans0 (Jeremy Evans)]

Only two weeks until the release of 2.5.0, and this hasn't been merged yet. I've tested and the patch still applies and the tests still pass.

[shyouhei (Shyouhei Urabe)]

Sorry, I missed this patch. Applied just now.

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Closed

Applied in changeset trunk|r61152.

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NEWS entry for FrozenError [Feature #13224]