Perimeter Method

Part of the Object Oriented Programming section of Coddy's Lua journey — lesson 58 of 70.

Challenge

Easy

Let's extend our Shape Manager by adding a :getPerimeter() method to both the Rectangle and Circle classes. Just like :getArea(), each shape calculates its perimeter differently, but they share the same method name—a perfect example of polymorphism in action.

You'll continue working with your existing files:

Shape.lua: Your base Shape class remains unchanged.
Rectangle.lua: Add a :getPerimeter() method that returns the rectangle's perimeter using the formula 2 × (width + height).
Circle.lua: Add a :getPerimeter() method that returns the circle's circumference using the formula 2 × π × radius. Use math.pi for π.
main.lua: Require both shape modules, read the dimensions from input, create one Rectangle and one Circle, then print six lines: the rectangle's name, area, and perimeter, followed by the circle's name, area, and perimeter.

Both shapes now have a complete interface with :getName(), :getArea(), and :getPerimeter()—all accessible through the same method names despite different implementations.

Input: Three lines—width (number), height (number), and radius (number).

Output: Six lines in order: rectangle's name, rectangle's area, rectangle's perimeter, circle's name, circle's area, circle's perimeter.

Try it yourself

-- Require the Rectangle module
local Rectangle = require('Rectangle')

-- Require the Circle module
local Circle = require('Circle')

-- Read width and height from input
local width = tonumber(io.read())
local height = tonumber(io.read())
local radius = tonumber(io.read())

-- Create a new Rectangle instance with the given dimensions
local rect = Rectangle:new(width, height)

-- Create a new Circle instance with the given radius
local circ = Circle:new(radius)

-- Print the rectangle's name, area, and perimeter
print(rect:getName())
print(rect:getArea())
print(rect:getPerimeter())

-- Print the circle's name, area, and perimeter
print(circ:getName())
print(circ:getArea())
print(circ:getPerimeter())