Mastering C# Collections: IEnumerable vs ICollection vs IList for Clean, Efficient Code

C# Collections: IEnumerable vs ICollection vs IList

When working with collections in C#, understanding the distinctions between IEnumerable<T>, ICollection<T>, and IList<T> is essential for writing scalable, maintainable, and performant applications.

1️⃣ IEnumerable<T>: Best for Iteration & Querying

Ideal Use Cases:

• Lazy evaluation for handling large datasets efficiently.
• Read-only access without modifying the collection.
• Supports LINQ queries for filtering and transformation.

Example:

using System.Collections.Generic;
IEnumerable<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
foreach (var number in numbers)
{
    Console.WriteLine(number); // Iterating forward only
}

2️⃣ ICollection<T>: Supports Modification & Sizing

Ideal Use Cases:

• Adding, removing, and clearing elements.
• Maintaining a Count property for efficient sizing.
• General data management operations within collections.

Example:

using System.Collections.Generic;
ICollection<int> numbers = new List<int> { 1, 2, 3 };
numbers.Add(4);  // Allowed in ICollection
numbers.Remove(2);
Console.WriteLine(numbers.Count); // Output: 3

3️⃣ IList<T>: Ordered & Index-Based Data Management

Ideal Use Cases:

• Maintaining order within collections.
• Direct index access and manipulation (numbers[0]).
• Managing lists used in UI, task management, and queues.

Example:

using System.Collections.Generic;
IList<string> names = new List<string> { "Alice", "Bob", "Charlie" };
names[1] = "David"; // Modify element at index 1
Console.WriteLine(names[1]); // Output: David

🚀 Why Choosing the Right Interface Matters

Understanding when to use IEnumerable, ICollection, or IList ensures:

• ✔ Optimized performance by avoiding unnecessary operations.
• ✔ Cleaner code that follows best practices.
• ✔ Scalability for large datasets and evolving applications.

Which collection interface do you use most—and why? Drop your thoughts in the comments below! 👇

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