From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2022-08-20T12:05:52+00:00
Subject: [ruby-core:109590] [Ruby master Feature#18969] Compare only method definitions for Method#== and UnboundMethod#==

Issue #18969 has been reported by Eregon (Benoit Daloze).

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Feature #18969: Compare only method definitions for Method#== and UnboundMethod#==
https://bugs.ruby-lang.org/issues/18969

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
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From https://bugs.ruby-lang.org/issues/18751#note-16

During the last dev meeting, @ko1 said Method#== should be "is it the same definition?" and I agree.
In #18751 I did it for zsuper methods (was necessary for compatibility).

But maybe we should do it for all methods.
Currently, Method#== and UnboundMethod#== compare the method definitions, but also (I think, the code is not that clear) on which receiver/class the method was fetched (klass for `klass.instance_method(name)` or `obj` for `obj.method(name)`).
(Maybe it checks the `#owner` too? I'm unsure)
This proposal is to do only the first: compare the method definitions.

So for instance:
```ruby
class A
  def foo
  end
end

class B < A
end

p A.instance_method(:foo) # => #<UnboundMethod: A#foo() method_eq.rb:2>
p A.instance_method(:foo).owner
p B.instance_method(:foo) # => #<UnboundMethod: B(A)#foo() method_eq.rb:2>
p B.instance_method(:foo).owner

p A.instance_method(:foo) == B.instance_method(:foo) # currently false, with proposal true
p A.new.method(:foo) == B.new.method(:foo) # currently false, with proposal true

# Current workaround needed to compare definitions:
m1, m2 = A.instance_method(:foo), B.instance_method(:foo)
p m1.owner.instance_method(m1.name) == m2.owner.instance_method(m2.name) # => true

m1, m2 = A.new.method(:foo), B.new.method(:foo)
p m1.owner.instance_method(m1.name) == m2.owner.instance_method(m2.name) # => true
```

I think this is the main usage of Method#== and UnboundMethod#==, to compare "is it the same method definition?".

OTOH, if we think this is not good for #== we could add `{Method,UnboundMethod}#same_definition?(other)`. `same_definition?` has the slight advantage that it could be true for `Method#same_definition?(UnboundMethod)` and vice versa.



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