bool_accessor.rb

class Module
  def bool_accessor(attribute)
    attr_accessor attribute
    define_method(attribute.to_s + "?") do
      !!send(attribute)
    end
  end
end

class Bar
  bool_accessor :has_foo
end

bar = Bar.new
puts bar.has_foo?
bar.has_foo = true
puts bar.has_foo?