[ruby-core:21425] Re: Proposal: Module#copy_method

I believe that methods (and blocks defined as methods via method_defined) a=
re somehow closed over the module that declares them so that "super" can fi=
nd the right module/class whose parent's method to call. At least they are =
in IronRuby :)

A simple copy of a method without changing binding to its declaring module =
therefore causes super to fail (or changes its semantics). I think this is =
the case even for module_function (I might have an example somewhere that d=
emonstrates it, will send it tomorrow if I find it). module_function "copie=
s" the method from declaring module to its singleton class, which is indeed=
 not derived from the declaring module, breaking super in some constructed =
cases.

Tomas

From: Yehuda Katz [mailto:[e-mail]]
Sent: Sunday, January 18, 2009 3:14 PM
To: [e-mail]
Subject: [ruby-core:21423] Re: Proposal: Module#copy_method

Just FYI, the define_method version fails if your method requires the use o=
f super. Observe:

class Zoo1
  def bar
    p "In superclass"
    1
  end
end

class Zoo2 < Zoo1
  def bar
    p "in Zoo2mod #{self}"
    super + 1
  end

  mod =3D Module.new do
    define_method(:bar, Zoo2.instance_method(:bar))
  end
  include mod

  def bar
    p "In bar"
    super + 1
  end
end

p Zoo2.new.bar

The above produces SystemStackError: stack level too deep, infinite-looping=
 in the original bar implementation on Zoo2. Also, it doesn't work on 1.9.

-- Yehuda
On Sun, Jan 18, 2009 at 2:32 PM, Charles Oliver Nutter <charles.nutter@sun.=
com<mailto:[e-mail]>> wrote:
Yehuda Katz wrote:
I'd like it to be possible to copy methods from one module to another. The =
rationale is that this feature would make it possible to modify existing me=
thods without being forced to resort to aliasing. Here's an implementation =
that works on 1.8 and 1.9:

Here's a pure-ruby version that works on an unmodified JRuby:

require 'jruby'

class Module
 def copy_method(mod, sym)
   # get JRuby DynamicMethod object from RubyMethod
   org.jruby.RubyMethod.field_reader :method
   ruby_method =3D mod.instance_method(sym)
   real_method =3D JRuby.reference(ruby_method).method

   # native methods may have memory/object layout needs
   raise "can't copy native method" if real_method.native?

   # Add it directly to the JRuby RubyModule self
   real_modcls =3D JRuby.reference(self)
   real_modcls.add_method(sym.to_s, real_method)
 end
end

- Charlie



--
Yehuda Katz
Developer | Engine Yard
(ph) 718.877.1325