Issue #21282 has been reported by sanjioh (Fabio Sangiovanni). ---------------------------------------- Bug #21282: `FrozenError` raised by `rb_error_frozen_object` should mention real class of frozen object https://bugs.ruby-lang.org/issues/21282 * Author: sanjioh (Fabio Sangiovanni) * Status: Open * ruby -v: ruby 3.5.0dev (2025-04-23T14:19:58Z fix-frozenerror-me.. 5c9dd42e27) +PRISM [x86_64-darwin24] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Hello everyone, I've noticed that the following snippets both raise `FrozenError`, but with different messages: ``` ruby Object.new.freeze.instance_variable_set(:@test, true) # can't modify frozen Object: #<Object:0x000000010b4d8aa8> (FrozenError) ``` ``` ruby Object.new.freeze.tap(&:singleton_class).instance_variable_set(:@test, true) # can't modify frozen #<Class:#<Object:0x0000000101538a98>>: #<Object:0x0000000101538a98> (FrozenError) ``` As you can see, the second example mentions the singleton class of the object, while I would expect `Object` to be mentioned in its place, as the first example does. From what I can see in `test/ruby/test_frozen_error.rb`, the expected behavior here should be to display the real class of the frozen object (as returned by `Kernel#class`), independently of the existence of a singleton class. I'm working on a PR that should fix this (will post the link in the comments in a moment). Cheers! -- https://bugs.ruby-lang.org/