It would be, if only it were true. Consider Array#delete_if or Array#pop, for example, although there are many others too.

Matz has written about this - https://www.ruby-forum.com/topic/176830#773946 - and said "The bang (!) does not mean "destructive" nor lack of it mean non destructive either. The bang sign means "the bang version is more dangerous than its non bang counterpart; handle with care".

This is one of the most commonly misunderstood things about Ruby in my experience (enough so that some library developers do apply a ! == destructive naming system) and would certainly make an equivalent "Ruby quirks" list IMHO! :-)