class User

  attr_accessor :name, :password

  def initialize new = {}
    hash = {:name => "name", :password => "password"}
    hash.merge! new
    hash.each {|name, value| instance_variable_set("@#{name}", value)}
  end

  def to_s
    "name: #{@name}, password: #{@password}"
  end
end

user = User.new :name => "my_name"

p user