Implementing one-shot methods in ruby

once_1.rb

# With this method, once(:method) has to be called after the method has been added
module Once
  def once(method)
    method = method.to_s
    class_eval <<-EVAL_END
      alias_method :#{method}_once, :#{method}
      def #{method}(*args)
        result = send('#{method}_once', *args)
        self.class.send(:remove_method, '#{method}_once')
        self.class.send(:remove_method, '#{method}')
        return result
      end
    EVAL_END
  end
end

once_2.rb

# With this method, once(:method) has to be called before the method has been added
module Once2
  def once(*methods)
    (@once_methods ||= []) << [*methods]
    @once_methods.flatten!
  end

  def method_added(method)
    return unless (@once_methods ||= []).include?(method)
    @once_methods.delete(method)

    old_method = instance_method(method)
    define_method(method) do |*args, &block|
      result = old_method.bind(self).call(*args, &block)

      self.class.send(:remove_method, method)

      result
    end
  end
end

sample_session.rb

# irb -r ./once_1.rb -r ./once_2.rb

class Foo
  extend Once

  def foo
    "bar"
  end

  once :foo
end

class Foo2
  extend Once2
  once :foo, :bar

  def foo
    "foo method"
  end

  def bar
    "bar method"
  end
end

ruby-1.9.2-p290 :002 > x = Foo.new
 => #<Foo:0x007f842216f168> 
ruby-1.9.2-p290 :003 > x.foo
 => "bar" 
ruby-1.9.2-p290 :004 > x.foo
NoMethodError: undefined method `foo' for #<Foo:0x007f842216f168>
  from (irb):4
  from /Users/development/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'
ruby-1.9.2-p290 :005 > x = Foo2.new
 => #<Foo2:0x007f84230068c0> 
ruby-1.9.2-p290 :006 > x.foo
 => "foo method" 
ruby-1.9.2-p290 :007 > x.foo
NoMethodError: undefined method `foo' for #<Foo2:0x007f84230068c0>
  from (irb):7
  from /Users/development/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'
ruby-1.9.2-p290 :006 > x.bar
 => "bar method" 
ruby-1.9.2-p290 :007 > x.bar
NoMethodError: undefined method `bar' for #<Foo2:0x007f84230068c0>
  from (irb):7
  from /Users/development/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'