42. Auto-implemented properties

In programming, brevity is a virtue. Auto-implemented properties in C# offer a streamlined approach to encapsulating a class’s data, cutting down on boilerplate code.

Properties in C# are a sort of combination between fields and methods. They represent a particular piece of a class’s data, but they also have built-in ways to control the access and modification of that data. Auto-implemented properties, provide a shorthand way to declare properties when no additional logic is required in the property accessors.

Let’s revisit our Car class and convert the speed field into an auto-implemented property.

public class Car
{
    public int Speed { get; private set; }

    public void Accelerate(int delta)
    {
        if (delta < 0)
            delta = 0; // min

        Speed += delta;
    }

    public void Brake(int delta)
    {
        if (delta < 0)
            delta = 0; // min
        else if (delta > Speed)
            delta = Speed; // max

        Speed -= delta;
    }
}

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

In this example, Speed is an auto-implemented property. The { get; private set; } part is a syntax shortcut for a property that can be read by anyone (public get accessor) but can only be modified by methods within the Car class (private set accessor). Behind the scenes, C# is creating a hidden, private backing field for storing the property’s value, much like the speed field in our previous examples. This means that we no longer need to manually write a public method called GetSpeed for object holders to be able to get access to the current speed.

Car car = new Car();
car.Accelerate(10);
Console.WriteLine(car.Speed); // Possible because get is marked as public.

10

Since we’ve marked the set accessor (also known as setter) of the property as private we still cannot set the value of Speed from outside the Car class. In many cases this means that Speed is still encapsulated. In later chapters we will however discuss why properties don’t always provide sufficient encapsulation.

Car car = new Car();
car.Speed = 10; // Not possible because set is marked as private.

(2,1): error CS0272: The property or indexer 'Car.Speed' cannot be used in this context because the set accessor is inaccessible

Auto-implemented properties are a powerful feature in C#, enabling you to write less code while preserving the encapsulation principle. As we move forward, we will look at cases where a property needs additional logic, leading us to manually implemented properties.