Enumerable.Append and Enumerable.Prepend extension methods

Another gem I found on StackOverflow today (I’ve been spending a lot of time there these last couple of days..), this time in the form of a question on how to append or prepend a single value to an IEnumerable<T>.

Greg provided an elegant solution to this particular problem, and here’s his answer:

public static IEnumerable<T> Append<T>(this IEnumerable<T> source, T item)
{
    foreach (T i in source)
        yield return i;

    yield return item;
}

public static IEnumerable<T> Prepend<T>(this IEnumerable<T> source, T item)
{
    yield return item;

    foreach (T i in source)
        yield return i;
}

Which you can use like this:

var all = GetHeaders().Append(GetData());

As others have stated, what’s so nice about this solution is that it does not mutate the original collection, instead it generates a new IEnumerbale<T>.

Enjoy what you’re reading? Subscribe to my newsletter and get more content on AWS and serverless technologies delivered straight to your inbox.


Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.


Check out my new course, Complete Guide to AWS Step Functions.

In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, design patterns and best practices.

Get Your Copy