internal Enumerator(ImmutableTrieListBase <T> list, int startIndex = -1, int count = -1, bool reversed = false)
{
Requires.NotNull(list, nameof(list));
Requires.Range(startIndex >= -1, nameof(startIndex));
Requires.Range(count >= -1, nameof(count));
Requires.Argument(reversed || count == -1 || (startIndex == -1 ? 0 : startIndex) + count <= list.Count, nameof(count), "The specified {0} and {1} do not produce a enumerable range.", nameof(startIndex), nameof(count));
Requires.Argument(!reversed || count == -1 || (startIndex == -1 ? list.Count - 1 : startIndex) - count + 1 >= 0, nameof(count), "The specified {0} and {1} do not produce a enumerable range.", nameof(startIndex), nameof(count));
_list = list;
_enumeratingBuilderVersion = GetCurrentVersion(list);
count = count == -1 ? list.Count : count;
_startIndex = startIndex >= 0 ? startIndex : (reversed ? list.Count - 1 : 0);
_endIndex = reversed ? _startIndex - count + 1 : _startIndex + count - 1;
_runningIndex = reversed ? _startIndex + 1 : _startIndex - 1;
_reversed = reversed;
_disposed = false;
}
private static int GetCurrentVersion(ImmutableTrieListBase <T> list) => (list is Builder builder) ? builder.Version : -1;
