design-activity.md

• What classes does each implementation include? Are the lists the same?

  • Implementation A includes the following classes:
    • CartEntry
    • ShoppingCart
    • Order
  • Implementation B include the same classes.

• Write down a sentence to describe each class.

  • CartEntry: Keeps track of individual items added to cart.
  • ShoppingCart: Keeps track of cartful of items.
  • Order: Calculates price of purchasing cartful of items.

• How do the classes relate to each other? It might be helpful to draw a diagram on a whiteboard or piece of paper.

  • An Order contains one ShoppingCart.
  • A ShoppingCart contains many CartEntry(s).

• What data does each class store? How (if at all) does this differ between the two implementations?

  • Implementation A:
    • CartEntry stores unit_price and quantity
    • ShoppingCart stores entries
    • Order stores SALES_TAX, cart, and total_price (and price of a single cart entry, although not explicitly stored)
  • Implementation B:
    • CartEntry stores unit_price, quantity, and price (of single CartEntry)
    • ShoppingCart stores entries and price (sum of all entries)
    • Order stores SALES_TAX, cart, and total_price

• What methods does each class have? How (if at all) does this differ between the two implementations?

  • Implementation A:
    • They all have initialize methods, and Order has a total_price method.
  • Implementation B:
    • They all have initialize methods, and they all have different price methods.

• Consider the Order#total_price method. In each implementation:

  • Is logic to compute the price delegated to "lower level" classes like ShoppingCart and CartEntry, or is it retained in Order?
  • Does total_price directly manipulate the instance variables of other classes?
    • Implementation A:
      • The logic to compute the price is not delegated to "lower level" classes
      • total_price directly manipulates the instance variables of other classes
    • Implementation B:
      • The logic to compute price is delegated to "lower level" classes
      • total_price does not directly manipulate the instance variables of other classes

• If we decide items are cheaper if bought in bulk, how would this change the code? Which implementation is easier to modify?

  • In this case, we would want to change the unit price of a CartEntry depending on the quantity. This would be easier to do in Implementation B's CartEntry#price method.

• Which implementation better adheres to the single responsibility principle?

  • Implementation B

• Bonus question once you've read Metz ch. 3: Which implementation is more loosely coupled?

  • Implementation B

• Changes to Hotel

  • Move validate_size to Block
    • Make max_rooms a constant
  • Date validation -- where to? (Interval/DateRange class? Parent class for Block & Reservation?)
  • Move create_block logic to Block (tough bc coupled)