Feature #15725: Proposal: Add Array#reverse_sort, #revert_sort!, #reverse_sort_by, and #reverse_sort_by!

• Status: Rejected
• Assignee: -
• Target version: -

[sikachu (Prem Sichanugrist)]

Hello,

I would like to propose four new methods: #reverse_sort, #revert_sort!, #reverse_sort_by, and #reverse_sort_by! to Array.

These methods provides the most efficient way for user to get a reversed sorted array by calling sort(_by) then .reverse!.

As a language designer, I believe that we should suggest the most efficient way to perform a certain action to user. By introduce these methods, we can discourage user to use them instead of do array.sort.reverse or array.sort {|a,b| b<=>a} which are less performant.

I've looked through Redmine, and I saw that there was a proposal to introduce a similar method to Enumerable in https://bugs.ruby-lang.org/issues/8422, but was somewhat rejected due to the complication with infinite Enumerable. Given that Array is finite, I think this is the best place for these methods to be implemented.

I've attached a patch to implement these methods based on other ary_sort related methods. Please let me know your thought on how I could improve them to be mergeable, as I am not proficient in writing C.

I'm looking forward to hear your thoughts about this proposal. Thank you very much.

[mame (Yusuke Endoh)]

• Related to Feature #12648: `Enumerable#sort_by` with descending option added

[shevegen (Robert A. Heiler)]

As this is a duplicate it may be best to discuss it in #12648.

I have not yet commented so just briefly; I am mostly neutral, can see
both ways. I think a slight problem is that the method names can be
a bit long and clumsy, especially #reverse_sort_by! - this is in my
opinion a bit too long.

I am also not completely sure whether we really need it. I myself usually
use .sort and .sort_by, and then apply .reverse afterwards. But I can also
understand people wanting to do all in one go; we just should see that the
method names are useful, if this is approved that is (see what matz wrote
in the other issue). But again, I have no real strong preference either
way.

[sikachu (Prem Sichanugrist)]

Thank you for your initial feedback. I would like to quote one thing:

I myself usually use .sort and .sort_by, and then apply .reverse afterwards.

That's definitely the reason why I submit this proposal, because array.sort.reverse will actually create new Array twice, meanwhile reverse! will just flip the array in-place and is a better way memory-wise. These methods will suggest programmers the most efficient way to do thing when they want to sort and reverse and Array, as I describe in the description of the ticket.

One alternative other than introducing these methods: I wonder if we can detect if a result of a sort operation is being passed to reverse right away in the chain, (e.g. detect if user is doing array.sort.reverse) and doing a in-place reverse instead. That seems complicated though, and I don't have enough knowledge of the interpreter to know if that sort of thing is possible.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

Those methods do not make me feel 'spark joy'. If you really care about the performance, use reverse! after sort!.

Matz.

[duerst (Martin Dürst)]

Clarified that .reverse! can/should be used for reverse order with commit 2a26c1ea24..7f79a86d8b.