From: "stuyam (Stuart Yamartino) via ruby-core" <ruby-core@...>
Date: 2024-02-15T22:23:47+00:00
Subject: [ruby-core:116784] [Ruby master Feature#20080] Introduce #bounds method on Range

Issue #20080 has been updated by stuyam (Stuart Yamartino).


Thanks for the feedback @matz! Is it the word `bounds` that you don't like in relation to the start and end values of a range? I personally think bounds or a boundary can be considered inclusive or exclusive which is why including `exclude_end?` as part of the array is useful context. But it really comes down to how you might define `bounds` so I understand if you feel it doesn't fit. Do you think `deconstruct` might make sense then to support pattern matching or just manually calling it for serialization or array deconstruction? Admittedly I am not super familiar with how pattern matching works so Im not as clear on how that part would work.

I still feel this would be useful for serializing ranges and deconstructing values out of ranges, but I understand if people don't see the value.

----------------------------------------
Feature #20080: Introduce #bounds method on Range
https://bugs.ruby-lang.org/issues/20080#change-106808

* Author: stuyam (Stuart Yamartino)
* Status: Open
* Priority: Normal
----------------------------------------
Followup Reference: #20027 

**Update 1/11/24:** (based on many wonderful suggestions!)

1. Call the method `#bounds`.
```ruby
first, last = (1..300).bounds # => [1, 300]
first, last = (300..1).bounds # => [300, 1]
first, last = (..300).bounds # => [nil, 300]
first, last = (1..).bounds # => [1, nil]
```

2. Add `exclude_end?` support so re-hydration of Range works:
```ruby
b = (1..2).bounds  #=> [1,2]
Range.new(*b)      #=> 1..2

b = (1...2).bounds #=> [1,2,true]
Range.new(*b)      #=> 1...2
```

I did a better job of outlining use cases in this comment below so I will let that speak for itself: https://bugs.ruby-lang.org/issues/20080#note-3

**Update: 2/13/24**
Browsing the ruby codebase I noticed that the `#as_json` method on Range (when you `require 'json/add/range'`) does something similar to what the `#bounds` method we are describing is doing: https://github.com/ruby/ruby/blob/master/ext/json/lib/json/add/range.rb#L34

```ruby
{
  JSON.create_id  => self.class.name,
  'a'             => [ first, last, exclude_end? ]
}
```

This tells me we are on the right track. Though the difference here is that `exclude_end?` is always included. I am thinking the `#bounds` should maybe always be including the `exclude_end?` piece rather than only include it if it's `true`. I am inclined to suggest always including the `exclude_end?` regardless of if it is true or false to avoid confusion or people ever calling `#last` on the `#bounds` results thinking it is the `#last` value where it could be the `#last` or `#exclude_end?` value depending on the type or range. This would still satisfy all of the use cases outlined in this comment: https://bugs.ruby-lang.org/issues/20080#note-3

**Therefore I think `#bounds` should just always return: `[ first, last, exclude_end? ]`**

**Original Proposal:**
This feature request is to implement a method called `#begin_and_end` on `Range` that returns an array of the first and last value stored in a range:
```ruby
(1..300).begin_and_end #=> [1, 300]

first, last = (300..1).begin_and_end
first #=> 300
last #=> 1
```
I believe this would be a great addition to Ranges as they are often used to pass around a single object used to hold endpoints, and this allows easier retrieval of those endpoints.
This would allow easier deconstruction into start and end values using array deconstruction as well as a simpler way to serialize to a more primitive object such as an array for database storage.
This implementation was suggested by @mame in my initial feature suggestion regarding range deconstruction: https://bugs.ruby-lang.org/issues/20027

This implementation would work similar to how `#minmax` works where it returns an array of two numbers, however the difference is that `#minmax` doesn't work with reverse ranges as @Dan0042 pointed out in the link above:
```ruby
(1..42).minmax #=> [1, 42]
(42..1).minmax #=> [nil, nil]
```




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