Feature #13574: Method redefinition warning

• Status: Open
• Assignee: -
• Target version: -

[tenderlovemaking (Aaron Patterson)]

Hi,

If I redefine a method like this, I get a warning:

class Foo
  def bar
  end
end

class Foo
  def bar
  end
end

If I alias the method to a different name, I don't get a warning:

class Foo
  def bar
  end
end

class Foo
  alias :foo :bar

  def bar
  end
end

I think this is expected. However, if I alias the method to itself, I don't get a warning:

class Foo
  def bar
  end
end

class Foo
  alias :bar :bar

  def bar
  end
end

I think this case should cause a warning.

[matthewd (Matthew Draper)]

As there's no other way to silence the redefinition warning (apart from removing the method first, which isn't atomic), the fact aliases silence it is very useful.

As a special case, aliasing it back to itself is particularly helpful for this purpose: it avoids polluting the method table with extra names, and is a clear indication we're not actually trying to give the method another name.

I don't know whether it was originally intended to work this way, but I think it is useful enough to keep. I also think a warning is unnecessary because it's not a likely error for a developer to make: there is no similar code that would make more sense.

[Eregon (Benoit Daloze)]

matthewd (Matthew Draper) wrote:

apart from removing the method first, which isn't atomic

What do you mean?
That remove_method + new definition is not atomic?

[matthewd (Matthew Draper)]

What do you mean?
That remove_method + new definition is not atomic?

Yes. Using remove_method + define_method, a concurrent thread may get a NoMethodError. In contrast, using alias_method + define_method, while the other thread could obviously call either the old or new definition (depending on exact timing), there will always be a method there.

[jeremyevans0 (Jeremy Evans)]

• Backport deleted (2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN)
• Tracker changed from Bug to Feature
• ruby -v deleted (ruby 2.5.0dev (2017-03-22 gc-compact 58059) [x86_64-darwin16])