[ruby-core:109602] [Ruby master Feature#18798] `UnboundMethod#==` with inherited classes

Issue #18798 has been updated by Eregon (Benoit Daloze).


I think we should do this, because I think the main purpose of {Method,UnboundMethod}#== is to find out if two methods have the same definition (or in other words, are equivalent in behavior).

I filed #18969 which is a duplicate.
That issue also suggests that if changing {Method,UnboundMethod}#== is not acceptable, then a new method could do that e.g. `{Method,UnboundMethod}#same_definition?(other)`.

----------------------------------------
Feature #18798: `UnboundMethod#==` with inherited classes
https://bugs.ruby-lang.org/issues/18798#change-98785

* 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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