From: "nathan.f77 (Nathan Broadbent)" Date: 2012-11-13T08:29:57+09:00 Subject: [ruby-core:49268] [ruby-trunk - Feature #7341][Open] Enumerable#associate Issue #7341 has been reported by nathan.f77 (Nathan Broadbent). ---------------------------------------- Feature #7341: Enumerable#associate https://bugs.ruby-lang.org/issues/7341 Author: nathan.f77 (Nathan Broadbent) Status: Open Priority: Low Assignee: Category: lib Target version: next minor Jeremy Kemper proposed Enumerable#associate during the discussion in #7297, with the following details: ------------------- Some background: #4151 proposes an Enumerable#categorize API, but it's complex and hard to understand its behavior at a glance. #7292 proposes an Enumerable#to_h == Hash[...] API, but I don't think of association/pairing as explicit coercion, so #to_h feels misfit. Associate is a simple verb with unsurprising results. It doesn't introduce ambiguous "map" naming. You associate an enumerable of keys with yielded values. Some before/after examples: Before: Hash[ filenames.map { |filename| [ filename, download_url(filename) ]}] After: filenames.associate { |filename| download_url filename } # => {"foo.jpg"=>"http://...", ...} Before: alphabet.each_with_index.each_with_object({}) { |(letter, index), hash| hash[letter] = index } After: alphabet.each_with_index.associate # => {"a"=>0, "b"=>1, "c"=>2, "d"=>3, "e"=>4, "f"=>5, ...} Before: keys.each_with_object({}) { |k, hash| hash[k] = self[k] } # a simple Hash#slice After: keys.associate { |key| self[key] } ------------------- It's worth noting that this would compliment ActiveSupport's Enumerable#index_by method: http://api.rubyonrails.org/classes/Enumerable.html#method-i-index_by #index_by produces '{ => el, ...}', while #associate would produce '{el => , ...}'. For cases where you need to control both keys and values, you could use '[1,2,3].map{|i| [i, i * 2] }.associate', or continue to use 'each_with_object({})'. -- http://bugs.ruby-lang.org/