From: "jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date: 2025-12-14T02:46:15+00:00
Subject: [ruby-core:124189] [Ruby Feature#21389] Simplify Set#inspect output

Issue #21389 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Open to Closed

zverok (Victor Shepelev) wrote in #note-5:
> Just noticed that on the latest `master` subclasses `#inspect` didn't change (unlike what @matz suggests here: https://bugs.ruby-lang.org/issues/21389#note-3):
> 
> ```ruby
> class MySet < Set
> end
> 
> p Set[1, 2, 3]   #=> Set[1, 2, 3]
> p MySet[1, 2, 3] #=> #<MySet: {1, 2, 3}>
> ```
> 
> Is it deliberate? (Working on docs for the new release.)

Yes, this is deliberate for backwards compatibility. Discussion in the GitHub PR: https://github.com/ruby/ruby/pull/15228

If you subclass from `Set::CoreSet` (which avoids adding backwards compatibility), the #inspect output follows the new Set output: https://github.com/ruby/ruby/pull/15228#discussion_r2539497376

The basic approach is that as much as possible, subclasses of Set behave as they did behavior. The only cases where the behavior isn't backwards compatible for Set subclasses is if the related methods accessed `@hash` (which no longer exists). In cases where `@hash` was accessed in stdlib Set, the backwards compatibility methods generally call `super` or another method.

Unless you need backwards compatibility with stdlib Set, I recommend subclassing from `Set::CoreSet` instead of `Set`.

----------------------------------------
Feature #21389: Simplify Set#inspect output
https://bugs.ruby-lang.org/issues/21389#change-115664

* Author: jeremyevans0 (Jeremy Evans)
* Status: Closed
* Assignee: jeremyevans0 (Jeremy Evans)
----------------------------------------
As Set is now a core collection class, it should have special inspect output.  Ideally, inspect output should be suitable to eval, similar to array and hash (assuming the elements are also suitable to eval):

```ruby
set = Set[1, 2, 3]
eval(set.inspect) == set # should be true
```

The simplest way to do this is to use the Set[] syntax:

```ruby
Set[1, 2, 3].inspect
# => "Set[1, 2, 3]"
```

I've submitted a pull request that implements this: https://github.com/ruby/ruby/pull/13488

The pull request deliberately does not use any subclass name in the output, similar to array and hash. I think it is more important that users know they are dealing with a set than which subclass:

```ruby
Class.new(Set)[]
# PR does: Set[]
#     not: #<Class:0x00000c21c78699e0>[]
```

However, it's easy to change the PR to use a subclass name if that is desired.



-- 
https://bugs.ruby-lang.org/
______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/