From: Su Zhang <zhangsu@...>
Date: 2011-04-18T07:37:21+09:00
Subject: Undefine Method Only Marks the Method Undefined

Hello,

According to the book Programming Ruby by Dave Thomas, "an
undefined method still exists - it is simply marked as being undefined."
Why is it not completely removed?

I find this somewhat related to the fact that an object still cannot be
dumped after "undefing" its singleton methods.

obj = Object.new

def obj.foo
end

p obj.respond_to? :foo  # => true

class << obj
  undef foo
end

p obj.respond_to? :foo  # => true

Marshal.dump(obj)       # => error

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