define_value_objects

💎 Encapsulate Data in Value Objects

For domain data that’s immutable and compared by value, build custom value objects. Implement eql? and hash so they behave predictably in collections.

class Money
  attr_reader :amount, :currency

  def initialize(amount, currency)
    @amount, @currency = amount, currency
    freeze
  end

  def ==(other)
    other.is_a?(Money) && amount == other.amount && currency == other.currency
  end
  alias eql? ==

  def hash
    [amount, currency].hash
  end
end

m1 = Money.new(100, 'USD')
m2 = Money.new(100, 'USD')
puts m1 == m2 # true