EnumerableX - Span and RSpan.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace FlashFormatting {
    public static class EnumerableX {
        //"today is nice".Span<char>(x => x != ' ') => (['t','o','d','a','y'], [' ','i','s',' ','n','i','c','e'])
        public static Tuple<T[], T[]> Span<T>(this IEnumerable<T> chain, Predicate<T> qualifier) {
            if (chain == null) {
                return null;
            }
            var chainArr = chain.ToArray();
            if (chainArr.Length == 0) {
                return new Tuple<T[], T[]>(new T[0], new T[0]);
            }
            var matchingRes = chainArr.TakeWhile(item => qualifier(item)).ToArray();
            T[] unmatchedRes;
            if (matchingRes.Length > 0) {
                unmatchedRes = chainArr.Skip(matchingRes.Length).ToArray();
            } else {
                unmatchedRes = chainArr;
            }
            return new Tuple<T[], T[]>(matchingRes, unmatchedRes);
        }

        //"today is nice".Span(x => x != ' ') => ("today", " is nice")
        public static Tuple<string, string> Span(this string str, Predicate<char> qualifier) {
            var tpl = str.Span<char>(qualifier);
            Debug.Assert(tpl.GetType() == typeof(Tuple<char[], char[]>));
            return new Tuple<string, string>(new String((char[])tpl.Item1), new String((char[])tpl.Item2));
        }


        //"today is nice".RSpan<char>(x => x != ' ') => (['e','c','i','n'], [' ','s','i',' ','y','a','d','o','t'])
        public static Tuple<T[], T[]> RSpan<T>(this IEnumerable<T> chain, Predicate<T> qualifier) => chain.Reverse().Span(qualifier);

        //"today is nice".RSpan(x => x != ' ') => ("ecin", " si yadot")
        public static Tuple<string, string> RSpan(this string str, Predicate<char> qualifier) {
            var tpl = str.RSpan<char>(qualifier);
            Debug.Assert(tpl.GetType() == typeof(Tuple<char[], char[]>));
            return new Tuple<string, string>(new String((char[])tpl.Item1), new String((char[])tpl.Item2));
        }
    }
}