module Hashie::Extensions::MethodOverridingWriter

def already_overridden?(name)
  method?("__#{name}")
end

def convert_key(key)
  key.to_s
end

def method?(name)
  methods.map(&:to_s).include?(name)
end

def method_missing(name, *args)
  if args.size == 1 && name.to_s =~ /(.*)=$/
    key = Regexp.last_match[1]
    redefine_method(key) if method?(key) && !already_overridden?(key)
    return self[convert_key(key)] = args.first
  end
  super
end

def redefine_method(method_name)
  eigenclass = class << self; self; end
  eigenclass.__send__(:alias_method, "__#{method_name}", method_name)
  eigenclass.__send__(:define_method, method_name, -> { self[method_name] })
end

def respond_to_missing?(name, include_private = false)
  return true if name.to_s.end_with?('=')
  super
end