Bug #7613: An Alias for a class method inherited from the Class class is not equal to the original method

• Status: Closed
• Assignee: -
• Target version: 1.9.3
• ruby -v: ruby 1.9.3p327 (2012-11-10) [i386-mingw32]

[zhangsu (Su Zhang)]

class Stream
  class << self
    alias_method :open, :new
  end
end

open = Stream.method(:open)
new = Stream.method(:new)
p open, new                   # => #<Method: Stream.new>, #<Method: Class#new>
p open.receiver, new.receiver # => Stream, Stream
p open == new                 # => false

Expect the last line to return true, but got false. According to the documentation for Method#==:

Two method objects are equal if they are bound to the same object and refer to the same method definition.

Here, open and new are all bound to Stream and I expect them to refer to the method definition too.

[shugo (Shugo Maeda)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r38638.
Su, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• proc.c (method_eq): fix the documentation to refer to owner.
  [ruby-core:51105] [Bug #7613]

• test/ruby/test_method.rb (test_alias_onwer): new test to confirm
  that `a == b' returns false if owners of a and b are different.

[shugo (Shugo Maeda)]

zhangsu (Su Zhang) wrote:

class Stream
  class << self
    alias_method :open, :new
  end
end

open = Stream.method(:open)
new = Stream.method(:new)
p open, new                   # => #<Method: Stream.new>, #<Method: Class#new>
p open.receiver, new.receiver # => Stream, Stream
p open == new                 # => false

Expect the last line to return true, but got false. According to the documentation for Method#==:

open == new returns false because their owners are different.

p [open.owner, new.owner] #=> [#<Class:Stream>, Class]

Two method objects are equal if they are bound to the same object and refer to the same method definition.

Here, open and new are all bound to Stream and I expect them to refer to the method definition too.

I've fixed the documentation of Method#== as follows:

Two method objects are equal if they are bound to the same
object and refer to the same method definition and their owners are the
same class or module.

[shugo (Shugo Maeda)]

shugo (Shugo Maeda) wrote:

open == new returns false because their owners are different.

p [open.owner, new.owner] #=> [#<Class:Stream>, Class]

I forgot to explain why Method#== returns false if owners are different.
If owners of methods are different, the behavior of super is different in the methods,
so Method#== should not return true for the methods.