ObjectSpace: added Clear method and unit test

src/Hydrogen/Collections/StreamMapped/IStreamMappedCollection.cs

@@ -1,11 +1,13 @@
 using System;
+using System.Collections;
 using Hydrogen.ObjectSpaces;
 
 namespace Hydrogen;
 
 public interface IStreamMappedCollection {
 	ObjectStream ObjectStream { get; }
 
+	void Clear();
 }
 
 public interface IStreamMappedCollection<TItem> : IStreamMappedCollection {

src/Hydrogen/Collections/StreamMapped/IStreamMappedDictionary.cs

@@ -28,4 +28,6 @@ public interface IStreamMappedDictionary<TKey, TValue> : IDictionary<TKey, TValu
 
 	void RemoveAt(long index);
 
+	new void Clear();
+
 }

src/Hydrogen/Collections/StreamMapped/IStreamMappedHashSet.cs

@@ -13,4 +13,5 @@
 namespace Hydrogen;
 
 public interface IStreamMappedHashSet<TItem> : ISet<TItem>, IStreamMappedCollection, ILoadable, IDisposable {
+	new void Clear();
 }

src/Hydrogen/Collections/StreamMapped/IStreamMappedList.cs

@@ -11,10 +11,12 @@
 
 namespace Hydrogen;
 
-public interface IStreamMappedList<TItem> : IExtendedList<TItem>,  IStreamMappedCollection<TItem>, ILoadable, IDisposable {
+public interface IStreamMappedList<TItem> : IExtendedList<TItem>, IStreamMappedCollection<TItem>, ILoadable, IDisposable {
 
 	IItemSerializer<TItem> ItemSerializer { get; }
 
 	IEqualityComparer<TItem> ItemComparer { get; }
 
+	new void Clear();
+
 }

src/Hydrogen/Merkle/FlatMerkleTree.cs

@@ -231,6 +231,7 @@ public override IEnumerable<byte[]> ReadRange(long index, long count) {
 		}
 
 		public override void UpdateRange(long index, IEnumerable<byte[]> items) {
+			Tools.Debugger.CounterA++;
 			Guard.ArgumentNotNull(items, nameof(items));
 			var itemsArr = items as byte[][] ?? items.ToArray();
 			Guard.Argument(itemsArr.All(x => x.Length == _parent._digestSize), nameof(items), "Improper digest size(s)");

src/Hydrogen/ObjectSpaces/ObjectSpace.cs

@@ -172,6 +172,14 @@ public void Delete<TItem>(TItem item) {
 		}
 	}
 
+	public void Clear() {
+		using (EnterAccessScope()) {
+			foreach(var dimension in Dimensions) {
+				dimension.Clear();
+			}
+		}
+	}
+
 	public void Commit()  {
 		using (EnterAccessScope()) {
 			// flush all cached changes
@@ -308,7 +316,7 @@ protected virtual IStreamMappedCollection BuildDimension(ObjectSpaceDefinition.D
 		// Get a comparer
 		var comparer = _comparerFactory.GetEqualityComparer(dimensionDefinition.ObjectType);
 
-		// construct the the collection
+		// construct the collection
 		var list = (IStreamMappedCollection)typeof(StreamMappedRecyclableList<>)
 			.MakeGenericType(dimensionDefinition.ObjectType)
 			.ActivateWithCompatibleArgs(

src/Hydrogen/ObjectSpaces/ObjectSpaceMerkleTreeIndex.cs

@@ -70,6 +70,7 @@ private void SubscribeToDimensionTreeChanges(int i) {
 		// Listen to underlying collection root changes (and track the handler for unsub later)
 		var capturedIndex = i;
 		void CollectionRootListener(byte[] oldValue, byte[] newValue) {
+			newValue ??= Hashers.ZeroHash(Inner.MerkleTree.HashAlgorithm); // merkle-root property will return null when changed to zero's
 			Inner.Update(capturedIndex, newValue);
 		}
 		dimensionMerkleTree.KeyStore.RootChanged += CollectionRootListener;

tests/Hydrogen.Tests/ObjectSpaces/ObjectSpacesTestBase.cs

@@ -80,6 +80,28 @@ public void LoadDoesntThrow() {
 
 	#endregion
 
+	#region Clear
+
+	[Test]
+	public void Clear_1() {
+		var folder = Tools.FileSystem.GetTempEmptyDirectory(true);
+		var accountComparer = CreateAccountComparer();
+		Account savedAccount, loadedAccount;
+		using (var scope = CreateObjectSpaceScope(folder, true)) {
+			var objectSpace = scope.Item;
+			savedAccount = CreateAccount();
+			objectSpace.Save(savedAccount);
+			objectSpace.Clear();
+			objectSpace.Commit();
+
+			foreach(var dim in objectSpace.Dimensions)
+				Assert.That(dim.ObjectStream.Count, Is.EqualTo(0));
+		}
+
+	}
+
+	#endregion
+
 	#region Commit
 
 	[Test]
@@ -124,7 +146,6 @@ public void RollbackNotThrows() {
 		Assert.That(objectSpace.Rollback, Throws.Nothing);
 	}
 
-
 	[Test]
 	public void Rollback() {
 		var folder = Tools.FileSystem.GetTempEmptyDirectory(true);