IList vs ICollection vs IEnumerable

https://www.linkedin.com/pulse/ienumerable-vs-icollection-idictionary-ilist-hasan-shahjahan/

What are IList, ICollection, and IEnumerable?

Before we dive into the differences between these interfaces, let's first define what they are and what they do.

IList:

The IList interface is used to represent a collection of items that can be accessed by index. It is a more specific version of the ICollection interface, which means that it has all the same functionality as ICollection but with additional features that allow you to access items by their index in the list.

ICollection:

The ICollection interface is used to represent a collection of items that can be modified. It provides functionality for adding, removing, and counting items in the collection.

IEnumerable: 

The IEnumerable interface is used to represent a collection of items that can be iterated over. It provides functionality for iterating over the items in the collection but does not provide any functionality for modifying the collection.

Differences between IList, ICollection, and IEnumerable

The key differences between these interfaces are their functionality and performance. Here's a breakdown of the main differences:

Functionality:

IList:

Provides functionality for accessing items by index and modifying the collection.

ICollection: 

Provides functionality for modifying the collection but does not provide functionality for accessing items by index.

IEnumerable:

Provides functionality for iterating over the items in the collection but does not provide any functionality for modifying the collection.

Performance:

IList:

Because IList provides functionality for accessing items by index, it can be faster than ICollection or IEnumerable when working with large collections. However, IList is also more memory-intensive because it stores the items in an array.

ICollection:

ICollection is generally slower than IList because it does not provide functionality for accessing items by index. However, ICollection is less memory-intensive because it does not store the items in an array.

IEnumerable:

Because IEnumerable only provides functionality for iterating over the items in the collection, it is generally slower than IList or ICollection. However, IEnumerable is the least memory-intensive because it does not store the items in an array.

When to use IList, ICollection, and IEnumerable

Now that we understand the differences between these interfaces, let's take a look at when to use each one.

Use IList when:

• You need to access items in the collection by their index.
• You need to modify the collection.

Use ICollection when:

• You need to modify the collection.
• You don't need to access items in the collection by their index.

Use IEnumerable when:

• You only need to iterate over the items in the collection.
• You don't need to modify the collection.

Conclusion

In summary, IList, ICollection, and IEnumerable are three key interfaces in C# that are used to represent collections of items. While these interfaces may seem similar, they have distinct differences in terms of their functionality and performance. Understanding these differences is important when deciding which interface to use for your specific needs. By using the right interface for the job, you can improve the performance and functionality of your C# applications.