[ruby-core:110209] [Ruby master Feature#18798] `UnboundMethod#==` with inherited classes

["mame (Yusuke Endoh)" <noreply@ruby-lang.org>]

Issue #18798 has been updated by mame (Yusuke Endoh).


> No class field anymore:
>
> ```
> #<UnboundMethod: M#foo() umethod_iclass.rb:2>
> #<UnboundMethod: M#foo() umethod_iclass.rb:2> (no visual difference)
> true
> [#<UnboundMethod: A#foo() umethod_iclass.rb:8>, #<UnboundMethod: B#foo() umethod_iclass.rb:14>]
> ```

This understanding is correct.

Discussed at the dev meeting. To the best of our knowledge, the receiver of instance_method is now only used in `UnboundMethod#inspect` (and `#to_s`). At the dev meeting, no one saw the significance of keeping track of this receiver. So @matz wants to discard the information and to change `#==`, `#eql?`, `#hash` (if needed), `#inspect`, and `#to_s` as you said.

----------------------------------------
Feature #18798: `UnboundMethod#==` with inherited classes
https://bugs.ruby-lang.org/issues/18798#change-99492

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
----------------------------------------
Now `UnboundMethod` for a same method from a superclass and an inherited class are not `==`.

```ruby
class C
  def foo = :C
  $mc = instance_method(:foo)
end

class D < C
  $md = instance_method(:foo)
end

p $mc == $md #=> false
p $mc.owner #=> C
p $mc.owner == $md.owner #=> true
p $mc.source_location == $md.source_location #=> true
p $mc.inspect #=> "#<UnboundMethod: C#foo() t.rb:3>"
p $md.inspect #=> "#<UnboundMethod: D(C)#foo() t.rb:3>"
```

How about to make it `UnboundMethod#==` return true for this case?
Rule: "return true if the UnboundMethod objects point to a same method definition" seems simple.

FYI: On aliased unbound methods point to a same method are `==`.


```ruby
class C
  def foo = :C
  alias bar foo
  $mfoo = instance_method(:foo)
  $mbar = instance_method(:bar)
end

p $mfoo, $mbar
#=> #<UnboundMethod: C#foo() t.rb:2>
#=> #<UnboundMethod: C#bar(foo)() t.rb:2>

p $mfoo == $mbar #=> true
```




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