Backport #9275
closed
Class.new(Hash)#reject warning is confusing and is issued in situations where I don't think it should be
Description
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 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).
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