[Mono-dev] Trivial Enumerable Optimizations

[Robert Jordan]

Jonathan Pryor wrote:
> So is it possible to further optimize the LongCount() extension method?
> Perhaps something like this?
> 
>     public static long LongCount<TSource> (this IEnumerable<TSource> source)
>     {
>        // as before...
>        ICollection<TSource> c = source as ICollection<TSource>;
>        if (c != null) {
>            try {
>                return c.Count;
>            }
>            catch {
>                // ignore; collection has > int.MaxValue elements, 
>                // so count manually below.
>            }
>        }
>        // as before...
>     }
> 
> This will suffer an obvious performance penalty if the collection has
> over int.MaxValue elements (assuming .Count throws an exception when
> that happens), but as most (currently all?) collections will have less
> than int.MaxValue elements, this should be a performance win.
> 
> Thoughts?

I'd check whether "source" is an array and return what
Array.GetLongLength returned.

Robert