Enumerable.Append and Enumerable.Prepend extension methods

Yan Cui

I help clients go faster for less using serverless technologies.

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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>.

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