Exercise 2.3 · 习题

Exercise 2.3: Implement a representation for

rectangles in a plane. (Hint: You may want to make use of Exercise 2.2.)

In terms of your constructors and selectors, create procedures that compute the

perimeter and the area of a given rectangle. Now implement a different

representation for rectangles. Can you design your system with suitable

abstraction barriers, so that the same perimeter and area procedures will work

using either representation?

练习 2.3：实现平面上矩形的一种表示。（提示：可以利用练习 2.2。）基于你的构造函数和选择函数，创建能计算给定矩形周长和面积的过程。接下来，再实现矩形的另一种表示。你能否通过设置合适的抽象屏障，使同一套周长和面积过程在两种表示下都能正常工作？