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Unoptimized IEnumerable <>. Last with predicate

The extension method public static TSource Last<TSource>(this IEnumerable<TSource> source)for IEnumerable<TSource>uses optimization for the type source IList<TSource>, so that it does not iterate over the entire sequence when it can simply step to the end using indexing.

IList<TSource> tSources = source as IList<TSource>;
if (tSources != null)
{
    int count = tSources.Count;
    if (count > 0)
    {
        return tSources[count - 1];
    }
}

I slightly modified the code so that it was readable by mroe, but the functionality remained the same.

Why is it public static TSource Last<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)also not optimized when it can explicitly start the iteration from the end of the sequence?

If there should be something that matches the predicate, and it is near the beginning of the sequence, I still need to iterate to the very end. If at the end there is something suitable, I no longer need to sort out, because I started from the end.

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IList<TSource> tSources = source as IList<TSource>;
if (tSources != null)
{
    int count = tSources.Count;
    if (count > 0)
    {
        for (int i = count - 1; i >= 0; i--)
        {
            if (predicate(tSources[i]))
            {
                return tSources[i];
            }
        }
    }
}
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