RecyclableLongList.VersionedEnumerator added

Recyclable.Collections/RecyclableLongList.VersionedEnumerator.cs

@@ -0,0 +1,97 @@
+using System.Collections;
+using System.Diagnostics.Contracts;
+
+namespace Recyclable.Collections
+{
+	public partial class RecyclableLongList<T>
+	{
+		public struct VersionedEnumerator : IEnumerator<T>
+		{
+#nullable disable
+			private static readonly T _default = default;
+#nullable restore
+
+			private static readonly bool _isReferenceType = !typeof(T).IsValueType;
+
+			private int _currentBlockIndex;
+			private int _currentItemIndex;
+			private readonly RecyclableLongList<T> _list;
+
+#nullable disable
+			private T _current;
+#nullable restore
+			public readonly T Current => _enumeratorVersion == _list._version ? _current : throw new InvalidOperationException();
+
+			private readonly ulong _enumeratorVersion;
+
+			public bool MoveNext()
+			{
+				if (_enumeratorVersion != _list._version)
+				{
+					throw new InvalidOperationException();
+				}
+
+				Contract.EndContractBlock();
+				var list = _list;
+
+				if (_currentBlockIndex < list._lastBlockWithData)
+				{
+					_current = list._memoryBlocks[_currentBlockIndex][_currentItemIndex];
+					if (_currentItemIndex + 1 < list._blockSize)
+					{
+						_currentItemIndex++;
+					}
+					else
+					{
+						_currentBlockIndex++;
+						_currentItemIndex = 0;
+					}
+
+					return true;
+				}
+				// Move to the next item if we're within block boundaries, otherwise report end of collection.
+				else if (list._longCount > 0 && _currentItemIndex < (list._nextItemIndex > 0 ? list._nextItemIndex : list._blockSize))
+				{
+					_current = list._memoryBlocks[_currentBlockIndex][_currentItemIndex];
+					_currentItemIndex++;
+					return true;
+				}
+
+				return false;
+			}
+
+#nullable disable
+			readonly object IEnumerator.Current => _enumeratorVersion == _list._version ? _current : throw new InvalidOperationException();
+#nullable restore
+
+			public VersionedEnumerator(RecyclableLongList<T> list)
+			{
+				_current = _default;
+				_currentBlockIndex = 0;
+				_currentItemIndex = 0;
+				_enumeratorVersion = list._version;
+				_list = list;
+			}
+
+			public void Reset()
+			{
+				if (_enumeratorVersion != _list._version)
+				{
+					throw new InvalidOperationException();
+				}
+
+				_current = _default;
+				_currentBlockIndex = 0;
+				_currentItemIndex = 0;
+			}
+
+			public void Dispose()
+			{
+				if (_isReferenceType)
+				{
+					_current = _default;
+				}
+			}
+		}
+	}
+}

Recyclable.Collections/RecyclableLongList.cs

@@ -1109,6 +1109,7 @@ namespace Recyclable.Collections
 		public Enumerator GetEnumerator() => new(this);
 		IEnumerator IEnumerable.GetEnumerator() => new Enumerator(this);
 		IEnumerator<T> IEnumerable<T>.GetEnumerator() => new Enumerator(this);
+		public VersionedEnumerator GetVersionedEnumerator() => new(this);
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
 		public int IndexOf(T item)