Hi, I would like to propose a new member for Enumerable class:
int IndexOf<T>(IEnumerable<T> source, T item, IEqualityComperer<T> comparer)
It’s useful to find the index of an item inside the source. Only IList has a similar method but it force me to completely materialize all the source. The implementation can enumerate list or, if the original source type is IList, call the IList.IndexOf method. If the source type is an Array we can call Array.IndexOf.
What do you think?