From: shannonskipper@gmail.com
To: ruby-core@ruby-lang.org
Subject: [ruby-core:81798] [Ruby trunk Feature#13683] Add strict Enumerable#single
Date: Wed, 28 Jun 2017 01:15:04 +0000 [thread overview]
Message-ID: <redmine.journal-65495.20170628011503.49802438081e7736@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-13683.20170627060807@ruby-lang.org
Issue #13683 has been updated by shan (Shannon Skipper).
shevegen (Robert A. Heiler) wrote:
> What would the results be for the following code? In ruby (I find
> it easier to read ruby code rather than the description actually):
>
> [].single
> [1].single
> [1,2].single
> [1,2,3].single
>
> {}.single
> {cat: 'Tom'}.single
> {cat: 'Tom', mouse: 'Jerry'}.single
>
> (And any other Enumerable objects I may have forgotten here.)
I wrote a quick implementation before realizing there was a link to a Rails PR. Here are the results of your examples (and one added):
~~~
module Enumerable
def single
if one?
first
else
if block_given?
yield
else
raise "wrong collection size (actual #{size || count}, expected 1)"
end
end
end
end
[].single
#!> RuntimeError: wrong collection size (actual 0, expected 1)
[1].single
#=> 1
[1,2].single
#!> RuntimeError: wrong collection size (actual 2, expected 1)
[1,2,3].single
#!> RuntimeError: wrong collection size (actual 3, expected 1)
{}.single
#!> RuntimeError: wrong collection size (actual 0, expected 1)
{cat: 'Tom'}.single
#=> [:cat, "Tom"]
{cat: 'Tom', mouse: 'Jerry'}.single
#!> RuntimeError: wrong collection size (actual 2, expected 1)
[].single { 42 }
#=> 42
~~~
----------------------------------------
Feature #13683: Add strict Enumerable#single
https://bugs.ruby-lang.org/issues/13683#change-65495
* 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/
next prev parent reply other threads:[~2017-06-28 1:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-13683.20170627060807@ruby-lang.org>
2017-06-27 6:08 ` [ruby-core:81779] [Ruby trunk Bug#13683] Add strict Enumerable#single dnagir
2017-06-27 10:18 ` [ruby-core:81788] [Ruby trunk Feature#13683] " eregontp
2017-06-27 20:05 ` [ruby-core:81793] " shevegen
2017-06-27 21:41 ` [ruby-core:81794] " Matthew Kerwin
2017-06-27 23:19 ` [ruby-core:81796] " mame
2017-06-28 1:15 ` shannonskipper [this message]
2017-06-28 6:22 ` [ruby-core:81803] " nobu
2017-06-30 13:57 ` [ruby-core:81874] " dnagir
2017-06-30 14:01 ` [ruby-core:81875] " dnagir
2017-07-24 0:26 ` [ruby-core:82140] " johncbackus
2017-09-25 9:05 ` [ruby-core:82983] [Ruby trunk Feature#13683][Feedback] " matz
2018-04-16 22:45 ` [ruby-core:86554] [Ruby trunk Feature#13683] " me
2018-04-24 12:40 ` [ruby-core:86665] " nobu
2018-07-26 20:40 ` [ruby-core:88129] " shannonskipper
2019-04-02 16:11 ` [ruby-core:92111] " lisa.ugray
2019-10-06 20:14 ` [ruby-core:95250] [Ruby master " jonathan
2019-10-07 2:23 ` [ruby-core:95254] " daniel
2019-10-17 5:59 ` [ruby-core:95382] " matz
2019-10-17 6:24 ` [ruby-core:95384] " ppyd
2019-10-17 7:24 ` [ruby-core:95388] " hanmac
2019-10-17 17:55 ` [ruby-core:95399] " daniel
2019-11-13 16:04 ` [ruby-core:95845] " kuchenbecker.k
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