From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2021-11-29T18:29:20+00:00
Subject: [ruby-core:106317] [Ruby master Feature#12084] `Class#instance`

Issue #12084 has been updated by Eregon (Benoit Daloze).


`#instance` seems a too generic name for such a rarely-needed meta-programming feature, I think `#singleton_instance` is better.

@justcolin it would result in `Array.singleton_class`, otherwise that would break the invariant of `#singleton_instance` being the reverse of `#singleton_class`.

A concrete use-case would be welcome.

----------------------------------------
Feature #12084: `Class#instance`
https://bugs.ruby-lang.org/issues/12084#change-94944

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
----------------------------------------
For meta-programming/debugging purposes, I would like to request the inverse of `Object#singleton_class`. Namely, a method that is called on a class that is a singleton class, and returns the object it is a singleton of. Since the `Singleton` module in the standard library http://ruby-doc.org/stdlib-2.3.0/libdoc/singleton/rdoc/Singleton.html assigns the method name `instance` to such classes, I think `Class#instance` should be the name for such feature.

~~~RUBY
Array.singleton_class.instance # => Array
"foo".singleton_class.instance # => "foo"
~~~

When the receiver is a class but is not a singleton class, then it should raise an error.

~~~RUBY
Array.instance # => error
~~~



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