text: // Defines a customer by their time to checkout
  #ifndef CUSTOMER_H
  #define CUSTOMER_H
  
  class Customer
  {
  private:
    size_t service_t {};                           // Time to checkout
  
  public:
    explicit Customer(size_t st = 10) :service_t {st}{}
  
    // Decrement time remaining to checkout
    Customer& time_decrement()
    {
      --service_t;
      return *this;
    }
    bool done() { return service_t == 0; }
  };
  #endif