From: nobu@ruby-lang.org
To: ruby-core@ruby-lang.org
Subject: [ruby-core:91749] [Ruby trunk Feature#14799] Startless range
Date: Mon, 11 Mar 2019 05:29:35 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-77025.20190311052934.f62209bb9274e780@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-14799.20180531075634@ruby-lang.org
Issue #14799 has been updated by nobu (Nobuyoshi Nakada).
`BDOT2` and `BDOT3` don't seem necessary.
----------------------------------------
Feature #14799: Startless range
https://bugs.ruby-lang.org/issues/14799#change-77025
* Author: zverok (Victor Shepelev)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version:
----------------------------------------
On introduction of endless range at #12912, "startless range" was discussed this way:
> @sowieso: Not having the opposite (`..5` and `..-2`) feels like this is rather a hack than a thoroughly planned feature.
> @duerst: I don't understand the need for a `..5` Range. The feature is called "endless range". Although mathematically, it's possible to think about startless ranges, they don't work in a program. Maybe some programming languages have `..5` as a shortcut for `0..5`, but that's in any way a usual, bounded, range with a start and an end. It's conceptually totally different from `5..`, which is a range with a start but no end, an unbound range.
In the context of that ticket (ranges used mostly for slicing arrays) having `..5` was indeed hard to justify, but there are other cases when `..5` being `-Infinity..5` is absolutely reasonable:
```ruby
case release_date
when ..1.year.ago
puts "ancient"
when 1.year.ago..3.months.ago
puts "old"
when 3.months.ago..Date.today
puts "recent"
when Date.today..
puts "upcoming"
end
log.map(&:logged_at).grep(..Date.new(1980)) # => outliers due to bad log parsing...
```
E.g., whenever case equality operator is acting, having startless range to express "below this value" is the most concise and readable way. Also, for expressing constants (mostly decorative, but very readable):
```ruby
# Celsius degrees
WORK_RANGES = {
..-10 => :turn_off,
-10..0 => :energy_saving,
0..20 => :main,
20..35 => :cooling,
35.. => :turn_off
}
```
In addition, my related proposal #14784 suggests that this kind of ranges could be utilized by more powerful clamp too:
```ruby
updated_at.clamp(..Date.today)
```
**Uncertainty points:**
* Would it be hard to add to parser? I am not sure, I am not very good at it :(
* Should `..` be a thing? I guess not, unless there would be convincing real-life examples, which for me it is hard to think of.
---Files--------------------------------
beginless-range.patch (3.55 KB)
--
https://bugs.ruby-lang.org/
next prev parent reply other threads:[~2019-03-11 5:29 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-14799.20180531075634@ruby-lang.org>
2018-05-31 7:56 ` [ruby-core:87313] [Ruby trunk Feature#14799] Startless range zverok.offline
2018-05-31 8:10 ` [ruby-core:87314] " shyouhei
2018-05-31 9:14 ` [ruby-core:87315] " zverok.offline
2018-05-31 9:31 ` [ruby-core:87316] " shyouhei
2018-05-31 9:51 ` [ruby-core:87317] " zverok.offline
2018-05-31 11:39 ` [ruby-core:87318] [Ruby trunk Feature#14799][Assigned] " mame
2018-05-31 13:01 ` [ruby-core:87320] [Ruby trunk Feature#14799] " janosch84
2018-06-04 11:10 ` [ruby-core:87388] " darkwiiplayer
2018-06-14 14:34 ` [ruby-core:87492] " zn
2018-06-14 15:16 ` [ruby-core:87494] " eregontp
2018-06-14 22:30 ` [ruby-core:87496] " mame
2018-06-15 17:14 ` [ruby-core:87500] " eregontp
2018-06-21 9:02 ` [ruby-core:87561] " knu
2019-03-11 5:17 ` [ruby-core:91747] " matz
2019-03-11 5:29 ` nobu [this message]
2019-04-03 8:16 ` [ruby-core:92123] " mame
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