When dealing with the Law of Demeter, what's an example of a situation where you'd need to change the consumer class, due to over-delegation?

Question

I often find myself doing lots of delegating.

In Ruby Science, it says:

Many delegate methods to the same object are an indicator that your object graph may not accurately reflect the real world relationships they represent.

and

If you find yourself writing lots of delegators, consider changing the consumer class to take a different object. For example, if you need to delegate lots of User methods to Account, it’s possible that the code referencing User should actually reference an instance of Account instead.

I don't really understand this. What is an example of how this would look in practice?

Answer 1

I think the author of that chapter wants to make clear, that, for example, writing:

class User
  def discounted_plan_price(discount_code)
    coupon = Coupon.new(discount_code)
    coupon.discount(account.plan.price)
  end
end

Notice account.plan.price, could be better done by using delegate on the user model, such as:

class User
  delegate :discounted_plan_price, to: :account
end

which allows you to write the following:

class User
  def discounted_plan_price(discount_code)
    account.discounted_plan_price(discount_code)
  end
end

class Account
  def discounted_plan_price(discount_code)
    coupon = Coupon.new(discount_code)
    coupon.discount(plan.price)
  end
end

Notice that we write plan.price, instead of account.plan.price, thanks to the delegate.

Good example, but there are many more.