２つのオブジェクトを全インスタンス変数の値で比較する

class User
  attr_reader :first_name, :last_name, :group

  def initialize(first_name, last_name, group)
    @first_name = first_name
    @last_name = last_name
    @group = group
  end 

  def ==(another)
    self.instance_variables.all? do |v|
      self.instance_variable_get(v) == another.instance_variable_get(v)
    end
  end
end

user1 = User.new("yamada", "taro", "A")
user2 = User.new("yamada", "taro", "A")
user3 = User.new("yamada", "taro", "B")

p user1 == user2 # => true
p user1 == user3 # => false