ForEachVariations.cs

        /// <summary>
        /// Custom function to perform looping operation.
        /// </summary>
        /// <typeparam name="T">type of ienumerable</typeparam>
        /// <param name="list">The list.</param>
        /// <param name="action">The action.</param>
        /// <returns>index value</returns>
        /// <exception cref="System.ArgumentNullException"> if the supplied action is null</exception>
        public static int ForEach<T>(this IEnumerable<T> list, Action<int, T> action)
        {
            if (action == null)
            {
                throw new ArgumentNullException("action");
            }

            var index = 0;

            foreach (var elem in list)
            {
                action(index++, elem);
            }

            return index;
        }

        /// <summary>
        /// Fors the each.
        /// </summary>
        /// <typeparam name="T">type of ienumerable</typeparam>
        /// <param name="enumeration">The enumeration.</param>
        /// <param name="action">The action.</param>
        public static void ForEach<T>(this IEnumerable<T> enumeration, Action<T> action)
        {
            foreach (T item in enumeration)
            {
                action(item);
            }
        }

Usage:

        // Remove extra leading and trailing spaces
        var tempVals = argument.FilesToDownload;
        tempVals.ForEach((i, item) => argument.FilesToDownload[i] = item.Trim());