validate arguments of instance method

argsvalidator.rb

module ArgsValidator

  def self.validate_args name, args, rules, klass
    ([args.length,rules.length].min).times do |i|
      arg = args[i]
      rule = rules[i]
      next if rule == :any
      rule = rule.class unless rule.class <= Class
      unless arg.class <= rule
        th = %w[st nd rd][i%10] || 'th'
        raise ArgumentError.new("#{i+1}#{th} argument of #{klass.name}##{name} must be #{rule} but passed #{arg.class.name}")
      end
    end
  end

  def validate_args name, *rules
    wraped_method = instance_method(name)
    define_method(name) do |*args|
      begin
        ArgsValidator.validate_args name, args, rules, self.class
      rescue ArgumentError => e
        4.times{ e.backtrace.shift }
        raise e
      end
      wraped_method.bind(self).call(*args)
    end
  end
  private :validate_args

end


if $0 == __FILE__

  class Neko
    extend ArgsValidator
    def nyan(count,how="nyan")
      count.times{ puts how }
    end
    validate_args :nyan, Integer, String
  end

  Neko.new.nyan(1,"wan")     # => pass (say wan)
  Neko.new.nyan(2)           # => pass (say nyan nyan)
  Neko.new.nyan("one","wan") # => ArgumentError

end