Why not inherit from List?

 

In C#, it's generally not recommended to directly inherit from the List<T> class, or any other collection type, due to potential issues with encapsulation, design, and potential for unintended behavior. Instead, you should prefer composition or extension methods to add functionality to existing collection classes.

Here's an example to illustrate why direct inheritance from List<T> might not be a good idea:

csharp

using System;
using System.Collections.Generic;

// Directly inheriting from List<T> (not recommended)
class MyList<T> : List<T>
{
    public new void Add(T item)
    {
        Console.WriteLine("Adding an item to MyList.");
        base.Add(item);
    }
}

class Program
{
    static void Main()
    {
        MyList<int> myList = new MyList<int>();
        myList.Add(42);  // Calls the overridden Add method

        List<int> list = myList;  // Implicit conversion
        list.Add(10);  // Calls the original List<int>'s Add method
    }
}

In this example, we create a custom MyList<T> class that inherits from List<T>. We override the Add method to provide a custom implementation. However, there are several problems with this approach:

1. Liskov Substitution Principle Violation: Inheriting from List<T> breaks the Liskov Substitution Principle, which states that objects of a derived class should be able to be used wherever objects of the base class can be used. Our custom MyList<T> behaves differently from List<T>, which can lead to unexpected behavior.

2. Inappropriate Use of Inheritance: Inheritance should be used for "is-a" relationships, and composition or extension methods are often more appropriate for adding behavior to existing classes.

3. Potential for Unintended Behavior: Users might not expect your custom list to behave differently from the built-in List<T>. This can lead to confusion and bugs.

Instead of inheriting from List<T>, consider using composition by creating a class that contains a private List<T> instance and exposes the required methods and properties. Alternatively, you can use extension methods to add functionality to existing collection types while keeping the separation of concerns intact.