How to get the index of an element in an IEnumerable?

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I’d question the wisdom, but perhaps:

source.TakeWhile(x => x != value).Count();

(using EqualityComparer<T>.Default to emulate != if needed) – but you need to watch to return -1 if not found… so perhaps just do it the long way

public static int IndexOf<T>(this IEnumerable<T> source, T value)
{
    int index = 0;
    var comparer = EqualityComparer<T>.Default; // or pass in as a parameter
    foreach (T item in source)
    {
        if (comparer.Equals(item, value)) return index;
        index++;
    }
    return -1;
}

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