Inheritance Best Practices

Vaibhav • September 10, 2025

In the previous article, we explored the object class - the root of all types in C#. Now that we understand how every type ultimately derives from object, it’s time to step back and look at how we design inheritance hierarchies in practice. Inheritance is a powerful tool in object-oriented programming, but it’s also one of the easiest to misuse. Poorly designed hierarchies can lead to fragile code, confusing APIs, and maintenance headaches. In this article, we’ll walk through best practices for using inheritance effectively in C#, and how to avoid common pitfalls.

Use inheritance to model “is-a” relationships

Inheritance should reflect a natural “is-a” relationship between types. For example, a Dog is an Animal, so it makes sense for Dog to inherit from Animal. But a DatabaseConnection is not a Logger, even if they share some behavior - in that case, composition or interfaces are better choices.

class Animal
{
    public virtual void Speak()
    {
        Console.WriteLine("Animal sound");
    }
}

class Dog : Animal
{
    public override void Speak()
    {
        Console.WriteLine("Woof!");
    }
}

This hierarchy makes sense because Dog is a kind of Animal. The base class defines shared behavior, and derived classes override it to specialize.

Favor composition over inheritance

Inheritance is useful, but it tightly couples the derived class to the base class. If you only need to reuse behavior, consider using composition instead - that is, include an instance of another class as a field, rather than inheriting from it.

class Engine
{
    public void Start() => Console.WriteLine("Engine started");
}

class Car
{
    private Engine _engine = new Engine();

    public void Drive()
    {
        _engine.Start();
        Console.WriteLine("Car is driving");
    }
}

Here, Car uses an Engine, but doesn’t inherit from it. This keeps the design flexible and avoids unnecessary coupling.

Keep base classes focused and minimal

A base class should define only the behavior that is truly common to all derived types. Avoid stuffing it with methods that only apply to some subclasses - this forces unrelated classes to inherit behavior they don’t need.

class Animal
{
    public virtual void Speak() { }
    public virtual void Fly() { } // Not all animals fly!
}

This design is flawed because not all animals can fly. A better approach is to define a separate interface or class for flying behavior.

interface IFlyable
{
    void Fly();
}

class Bird : Animal, IFlyable
{
    public override void Speak() => Console.WriteLine("Tweet");
    public void Fly() => Console.WriteLine("Bird is flying");
}

Now only birds implement Fly(), and the base class remains clean and focused.

Use virtual methods for extensibility

If you expect derived classes to customize behavior, mark methods as virtual in the base class. This allows subclasses to override them. If you don’t want a method to be overridden, leave it non-virtual.

class Report
{
    public virtual void Generate()
    {
        Console.WriteLine("Generating base report");
    }
}

class SalesReport : Report
{
    public override void Generate()
    {
        Console.WriteLine("Generating sales report");
    }
}

This pattern allows each subclass to customize the report generation logic while still using a common interface.

Use sealed classes and methods to prevent inheritance

If a class is not designed for inheritance, mark it as sealed. This prevents other classes from inheriting it. Similarly, you can seal individual methods to prevent further overriding.

sealed class Logger
{
    public void Log(string message)
    {
        Console.WriteLine($"Log: {message}");
    }
}

This communicates your intent clearly and allows the runtime to optimize method calls more aggressively.

Avoid deep inheritance hierarchies

Deep inheritance trees are hard to understand and maintain. Prefer flat hierarchies with fewer levels. If you find yourself creating many layers of subclasses, consider refactoring with composition or interfaces.

class A { }
class B : A { }
class C : B { }
class D : C { } // Too deep!

This design is fragile and difficult to reason about. Instead, try to flatten the hierarchy or break it into smaller, focused components.

Use abstract classes to enforce contracts

An abstract class defines a contract that derived classes must fulfill. It can include both abstract members (no implementation) and concrete members (with implementation). Use abstract classes when you want to provide shared logic while enforcing certain behaviors.

abstract class Shape
{
    public abstract double Area();
    public void Describe() => Console.WriteLine("This is a shape");
}

class Rectangle : Shape
{
    public double Width, Height;
    public Rectangle(double w, double h) { Width = w; Height = h; }

    public override double Area() => Width * Height;
}

This pattern ensures that all shapes implement Area(), while sharing common behavior like Describe().

Use interfaces for capabilities

Interfaces are ideal for defining capabilities that can be added to any class, regardless of its inheritance hierarchy. For example, IComparable, IDisposable, and IEnumerable are common interfaces in .NET.

interface IPrintable
{
    void Print();
}

class Invoice : IPrintable
{
    public void Print()
    {
        Console.WriteLine("Printing invoice...");
    }
}

This allows you to treat any IPrintable object uniformly, regardless of its class hierarchy.

Design for substitution

The Liskov Substitution Principle states that derived classes should be usable wherever the base class is expected. This means you should avoid breaking expectations in overridden methods.

class Bird
{
    public virtual void Fly() => Console.WriteLine("Flying");
}

class Penguin : Bird
{
    public override void Fly() => throw new NotSupportedException("Penguins can't fly");
}

This violates substitution - a Penguin is a Bird, but it breaks the expected behavior of Fly(). A better design would separate flying behavior into an interface.

Document inheritance expectations

If your class is intended to be inherited, document which methods are meant to be overridden and how. Use XML comments to describe the contract and expectations. This helps other developers understand how to extend your class safely.

/// <summary>
/// Base class for all reports.
/// Override Generate() to customize report logic.
/// </summary>
class Report
{
    public virtual void Generate() { }
}

Clear documentation reduces misuse and makes your APIs easier to work with.

Summary

Inheritance is a powerful tool, but it must be used with care. You’ve learned how to model “is-a” relationships, when to prefer composition, how to use virtual and sealed methods, and how to design clean, maintainable hierarchies. You’ve also seen how abstract classes and interfaces support flexible design, and how to avoid common pitfalls like deep hierarchies and broken substitution. By following these best practices, you’ll write object-oriented code that is robust, extensible, and easy to understand.

In the next article, we’ll explore Multiple Interface Implementation - how to implement multiple interfaces in a single class, and how to resolve conflicts when method names overlap.