Issue #9275 has been reported by myronmarston (Myron Marston). ---------------------------------------- Bug #9275: Class.new(Hash)#reject warning is confusing and is issued in situations where I don't think it should be https://bugs.ruby-lang.org/issues/9275 Author: myronmarston (Myron Marston) Status: Open Priority: Normal Assignee: Category: Target version: ruby -v: ruby 2.1.0dev (2013-12-20 trunk 44301) [x86_64-darwin12.0] Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN Consider this script: ``` $VERBOSE = true Class.new(Hash).new.reject { } ``` When I run this with 2.1.0-rc1, I get the following output: ``` foo.rb:2: warning: copying unguaranteed attributes: {} foo.rb:2: warning: following atributes will not be copied in the future version: foo.rb:2: warning: subclass: #<Class:0x007f91bb89dda8> ``` This warning is confusing. I've been using ruby full time for ~ 5 years and I have no idea what "unguaranteed attributes" means. In addition, I don't think this warning should be issued in this case at all. According to the NEWS entry[1] and #9223, this warning is intended for cases where there is extra state (instance variables, default proc, etc) that will not be copied in the future...but in this case, it's a subclass of Hash with no extra state or behavior. Why should it warn in this case? As things stand now, if you want to have a warning-free gem, you can no longer subclass hash if you call #reject on it or expose it as part of your public API (as end users may call #reject on it). [1] https://github.com/ruby/ruby/blob/9881a183bde20d1c174d33d8a2f637e9c092a08b/NEWS#L136-L141 -- http://bugs.ruby-lang.org/