From: shannonskipper@... Date: 2020-10-06T21:06:28+00:00 Subject: [ruby-core:100316] [Ruby master Feature#13683] Add strict Enumerable#single Issue #13683 has been updated by shan (Shannon Skipper). ``` ruby [42] in [sole]; sole #=> 42 [] in [sole]; sole #!> NoMatchingPatternError ([]) [42, 43] in [sole]; sole #!> NoMatchingPatternError ([42, 43]) ``` For Arrays, pattern matching seems reasonable. Wouldn't that not work for other Enumerable collections? ``` ruby Set.new([42]) in [sole]; sole #!> NoMatchingPatternError (#) ``` It seems it an Enumerable# method would be more slick and nice for method chaining. ``` ruby Set.new([42]).sole #=> 42 Set.new([42]).sole.digits #=> [2, 4] ``` ---------------------------------------- Feature #13683: Add strict Enumerable#single https://bugs.ruby-lang.org/issues/13683#change-87897 * Author: dnagir (Dmytrii Nagirniak) * Status: Feedback * Priority: Normal ---------------------------------------- ### 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: