method defined on the eigenclass shadows the instance method

ruby_metaclass_shadow.rb

# method defined on the eigenclass shadows the instance method

require 'pp'

class A
  def foo; "A"; end
end

a1 = A.new
a2 = A.new

mk = class << a1
self
end

pp mk.object_id == a1.object_id #=> false

class << a1
def foo; "meta"; end
end

pp a1.foo #=> "meta"
pp a2.foo #=> "A"

__END__

ruby 1.9.3p327 (2012-11-10 revision 37606) [x86_64-darwin10.8.0]
false
"meta"
"A"