ImmutableList vs. List in C#

In C#, ImmutableList<T> and List<T> are collections that provide similar functionality with key differences in mutability, performance, and use cases. Understanding these distinctions helps you choose the right collection for your application's needs. This article compares ImmutableList<T> and List<T>, highlighting their unique features and practical usage.

Key Differences

1. Mutability

• ImmutableList: Once created, the list cannot be modified. Any operation that appears to modify the collection actually returns a new instance with the requested changes, leaving the original list intact.
• List: Allows in-place modification of items through methods like Add, Remove, and Insert.

2. Thread Safety

• ImmutableList: Naturally thread-safe since the collection cannot be changed after creation. Multiple threads can read the same list without synchronization.
• List: Not thread-safe by default. Modifying a List concurrently requires manual synchronization to avoid data corruption.

3. Performance

• ImmutableList: Requires more memory and processing time due to its need to return new instances on modification. Suitable for scenarios with many reads but fewer writes.
• List: Performs faster for frequent modifications because changes are made directly to the same collection.

4. Use Cases

• ImmutableList: Ideal for applications with high-read and low-write operations, and where thread safety or data integrity is essential.
• List: Better suited for applications requiring frequent or rapid modifications due to its direct editing capabilities.

Example: Comparing ImmutableList and List

Adding Elements to ImmutableList

using System;
using System.Collections.Immutable;

public class ImmutableListExample
{
    public static void Main()
    {
        // Create an empty immutable list
        ImmutableList<int> numbers = ImmutableList<int>.Empty;

        // Add items, each Add returns a new list
        ImmutableList<int> updatedNumbers = numbers.Add(1).Add(2).Add(3);

        Console.WriteLine("ImmutableList:");
        foreach (int number in updatedNumbers)
        {
            Console.WriteLine(number);
        }
    }
}

Adding Elements to List

using System;
using System.Collections.Generic;

public class ListExample
{
    public static void Main()
    {
        // Create an empty list
        List<int> numbers = new List<int>();

        // Add items directly to the list
        numbers.Add(1);
        numbers.Add(2);
        numbers.Add(3);

        Console.WriteLine("List:");
        foreach (int number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}

Conclusion

When choosing between ImmutableList<T> and List<T>, consider the mutability, performance, and concurrency requirements of your application. While ImmutableList<T> excels in scenarios requiring data integrity and thread safety, List<T> remains a versatile option for rapid and frequent modifications.