From: mathew Date: 2011-01-22T02:43:44+09:00 Subject: [ruby-core:34758] Re: Hash iteration contract (was Re: Let's begin a talk for "1.8.8" -- How's needed for surviving 1.8?) On Thu, Jan 20, 2011 at 09:53, Zeno Davatz wrote: > We are just working on our Ruby 1.9 application and we just found another > consistency problem in Ruby 1.9. The way Hashes are iterated in Ruby 1.9.1 > is different from the way Hashes are iterated in Ruby-1.9.2. I brought this up in December: I wrote: > Is it really a good idea to specify the order in which keys are > returned? That could have major implications later on if someone wants > to rewrite Hash to increase performance. I still think it's a bad idea to guarantee any particular ordering when iterating hashes. For example, Java's HashMap class says: > This class makes no guarantees as to the order of the map; in particular, it does > not guarantee that the order will remain constant over time. My feeling is that if people want to iterate through hash keys or hash values in a particular order, they should sort them explicitly, or use a more special purpose SortedHash class. The rest of the time we should be able to use a Hash class that offers no key or value ordering guarantees, but is as fast as possible as a result. mathew --