From: me@... Date: 2018-04-16T22:45:46+00:00 Subject: [ruby-core:86554] [Ruby trunk Feature#13683] Add strict Enumerable#single Issue #13683 has been updated by IotaSpencer (Ken Spencer). matz (Yukihiro Matsumoto) wrote: > Hmm, I don't like the name `single`. Besides that, I think it may be useful for database access, but I don't see the use-case of this method for generic Enumerable. > > Matz. I think of single as a method towards mutual exclusivity. If an Array or Enumerable from another expression should only have a single element, then this gives the process a much faster setup and possible rescue, as I currently have one of my projects checking for the existence of 3 headers, `X-GitHub-Event`, `X-GitLab-Event`, and `X-Gogs-Event`, and I found the easiest way was to use `one` from Enumerable, but I wanted it to error out so that I could catch it with the rest of my raised exceptions from other errors that arise in the handling of the request. How about these for suggestions. `one_or_raise` `one_or_nothing` Part of my code for context. ~~~ ruby events = {'github' => github, 'gitlab' => gitlab, 'gogs' => gogs } events_m_e = events.values.one? case events_m_e when true event = 'push' service = events.select { |key, value| value }.keys.first when false halt 400, {'Content-Type' => 'application/json'}, {message: 'events are mutually exclusive', status: 'failure' }.to_json else halt 400, {'Content-Type' => 'application/json'}, {'status': 'failure', 'message': 'something weird happened' } end ~~~ ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-71494 * Author: dnagir (Dmytrii Nagirniak) * Status: Feedback * Priority: Normal * Assignee: * Target version: ---------------------------------------- ### Summary This is inspired by other languages and frameworks, such as LINQ's [Single](https://msdn.microsoft.com/en-us/library/bb155325%28v=vs.110%29.aspx) (pardon MSDN reference), which has very big distinction between `first` and `single` element of a collection. - `first` normally returns the top element, and the developer assumes there could be many; - `single` returns one and only one element, and it is an error if there are none or more than one. We, in Ruby world, very often write `fetch_by('something').first` assuming there's only one element that can be returned there. But in majority of the cases, we really want a `single` element. The problems with using `first` in this case: - developer needs to explicitly double check the result isn't `nil` - in case of corrupted data (more than one item returned), it will never be noticed `Enumerable#single` addresses those problems in a very strong and specific way that may save the world by simply switching from `first` to `single`. ### Other information - we may come with a better internal implementation (than `self.map`) - better name could be used, maybe `only` is better, or a bang version? - re-consider the "block" implementation in favour of a separate method (`single!`, `single_or { 'default' }`) The original implementation is on the ActiveSupport https://github.com/rails/rails/pull/26206 But it was suggested to discuss the possibility of adding it to Ruby which would be amazing. -- https://bugs.ruby-lang.org/ Unsubscribe: