Mark Chavez

Learning how to learn.

Tell, Don't Ask

May 29, 2017

Rubyists often write a block of code that is similar to the one below.

account = Account.new
account.balance = 5_000

if account.balance > 2_000
  account.buy_television!
end

This is a code smell. Here’s a better way to do it.

account = Account.new
account.buy_television!

The above example is more direct. It doesn’t ask. It tells object what to do.

Another bad example.

cards = get_credit_cards_for(customer)

if cards.all?(&:active)
  PurchaseOrder.create(customer)
end

The better version.

class PurchaseOrder
  def self.create(customer)
    create_transaction if customer.all_cards_active?
  end
end

PurchaseOrder.create(customer)

In OOP, we want to tell objects what needs to be done, not ask them first.