From: johncbackus@... Date: 2017-07-24T00:26:06+00:00 Subject: [ruby-core:82140] [Ruby trunk Feature#13683] Add strict Enumerable#single Issue #13683 has been updated by backus (John Backus). +1 to this proposal!! I have a `Util.one(...)` method in a half dozen or more projects. IMO `#one` is a nicer name than `#single`. [ROM](https://github.com/rom-rb/rom/blob/6016d323ca0a2aa38167e84a4eb2da0384e75b13/core/lib/rom/relation/loaded.rb#L49-L77) exposes an interface I like when reading results from the db: - `#one!` - raise an error unless the result's `#size` is *exactly* `1` - `#one` - raise an error if the result's `#size` is greater than `1`. Return the result of `#first` otherwise (so an empty result returns `nil`). I don't think the implementation should use the `#one?` predicate though. It would be confusing if `[nil, true, false].single` gave you `nil` instead of raising an error. ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-65898 * Author: dnagir (Dmytrii Nagirniak) * Status: Open * 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: