Permutations of a string, with iterative algorithm

PermutationsItertive.cs

private static IEnumerable<string> PermutationsIterative(string s)
        {
            var permutations = new List<(string permutation, string rest)>
            {
                ("", s)
            };

            while (true)
            {
                if (permutations.All(p => p.rest == ""))
                    return permutations.Select(p => p.permutation);

                permutations = permutations.SelectMany(p =>
                    p.rest.Select(c =>
                    (
                        p.permutation + c,
                        p.rest.RemoveChar(c)
                    ))).ToList();
            }
        }