## 26.7 Case Study: Putting Patterns to Work (cont.)

- Derived classes implement the virtual functions
- `get_total_price` is defined in the `Item` class:

  >     double Item::get_total_price() const
  >     {
  >        return get_quantity() * get_unit_price();
  >     }

- A generic item can't compute quantity or unit price, but it knows that the total price is their product - TEMPLATE METHOD pattern

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