Lab: Manually implemented properties

Objective

In this exercise, we will transform a traditional method-based approach to managing class state into a more modern, property-based one using manually implemented properties. This will involve refactoring the code to replace public methods that directly manipulate fields with properties that encapsulate the logic for setting and getting field values.

Provided Code

Carefully review the provided code. Notice that the Car class manages its speed state using a private field and two public methods, IncreaseSpeed and DecreaseSpeed. This is a common pattern, but it doesn’t take advantage of C#’s property feature.

class Car
{
    private int speed;

    public void IncreaseSpeed(int delta)
    {
        if (speed + delta < 0)
            speed = 0;
        else if (speed + delta > 200)
            speed = 200;
        else
            speed += delta;
    }

    public void DecreaseSpeed(int delta)
    {
        if (speed - delta < 0)
            speed = 0;
        else if (speed - delta > 200)
            speed = 200;
        else
            speed -= delta;
    }

    public int GetSpeed()
        => speed;
}

The below script needs to be able to find the current output cell; this is an easy method to get it.

Instructions

Step 1: Introduce the Speed property

Refactor the Car class by removing all instance methods and introduce a manually implemented property named Speed. The logic that we removed should now be part of the property’s set or get accessors.

Step 2: Test your refactored code

Ensure that the logic within the set accessor of your new Speed property maintains the same rules: speed cannot go below 0 and cannot exceed 200.

Car saab = new Car();

saab.Speed += 999;
Console.WriteLine(saab.Speed == 200);

saab.Speed -= 999;
Console.WriteLine(saab.Speed == 0);

True

True

Step 3: Introduce a MaxSpeed property

Add a new (automatically implemented) property called MaxSpeed to the Car class. Its type should be int. This property should have a public get accessor and a private set accessor. Add a constructor that takes a single parameter of type int. This value should be used to set the MaxSpeed of the Car object.

Car tractor = new Car(20);

tractor.Speed += 999;
Console.WriteLine(tractor.Speed == tractor.MaxSpeed);

tractor.Speed -= 999;
Console.WriteLine(tractor.Speed == 0);

True

True

tractor.MaxSpeed = 200; // Should raise exception!

(1,1): error CS0272: The property or indexer 'Car.MaxSpeed' cannot be used in this context because the set accessor is inaccessible

Challenge

Add a bool property called EcoMode that, when true, changes the get:er of the Speed property to return a value that is 80% below the actual speed to simulate fuel-saving measures.