Course of Raku / Addendum 🆕 / Types and text machines / Objects and classes / Exercises

Shapes sharing a role

Problem

Define a Shape role that requires an area method, then make Circle and Square classes that do the role.

Write a describe subroutine whose parameter is typed as Shape, so it accepts any shape and refuses anything that is not one. It should print the shape’s area labelled with its class name. Call it for a circle of radius 2 and a square of side 3.

The subroutine never checks which kind of shape it received: because its parameter is a Shape, the object is guaranteed to have an area method, so the same .area call works on whichever shape comes in. That is what the role gives you — a single type you can require, and one piece of code that treats every class doing it uniformly.

Example

The program prints:

Circle: 12.56636
Square: 9

Solution

✅ See the solution

Course navigation

← Solution: A bank account   |   Solution: Shapes sharing a role →