2024-04-08 週の読んだ記事 (コードレビュー/RSpec flaky/技術駆動/目的駆動名前設計/完全コンストラクタ/Tell, Don't Ask

class Money
  ALLOWED_CURRENCY = [:yen]
  attr_reader :amount, :currency

  def initialize(amount:, currency:)
    if amount < 0
      raise ArgumentError.new('金額は0以上を入力してください')
    end

    if currency.nil?
      raise ArgumentError.new('通貨単位を入力してください')
    end

    unless ALLOWED_CURRENCY.include?(currency.to_sym)
      raise ArgumentError.new("#{currency}は許可されていない通貨単位です")
    end

    @amount = amount
    @currency = currency
    self.freeze #イミュータブル化
  end

  def add(other)
    if @currency != other.currency
      raise ArgumentError.new('通貨単位が違います')
    end

    added = @amount + other.amount
    Money.new(amount: added, currency: @currency)
  end
end

# minus_money = Money.new(amount: -1,  currency: 'yen')
# NG 金額が マイナス
# nil_currency_money = Money.new(amount: 100,  currency: nil)
# NG 通貨単位がnil

money = Money.new(amount: 100,  currency: 'yen')
money.add(Money.new(amount: 500, currency: 'yen'))
# OK