Make IPersistentCollection.GetSnapshot() return object instead of ICollection. Some of the implementations return sets, and when those are BCL sets they don't implement non-generic ICollection. Since the contents of the snapshots are never accessed outside each type of persistent collection (and probably never should be), we might as well make it a completely opaque object.

Author: oskarb

src/NHibernate/Collection/AbstractPersistentCollection.cs

@@ -797,7 +797,7 @@ public virtual object GetIdentifier(object entry, int i)
 
 		public abstract IEnumerable Entries(ICollectionPersister persister);
 
-		public abstract ICollection GetSnapshot(ICollectionPersister persister);
+		public abstract object GetSnapshot(ICollectionPersister persister);
 
 		public abstract bool EqualsSnapshot(ICollectionPersister persister);
 

src/NHibernate/Collection/Generic/PersistentGenericMap.cs

@@ -30,7 +30,7 @@ public PersistentGenericMap(ISessionImplementor session, IDictionary<TKey, TValu
 			gmap = map;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 			Dictionary<TKey, TValue> clonedMap = new Dictionary<TKey, TValue>(map.Count);

src/NHibernate/Collection/Generic/PersistentGenericSet.cs

@@ -87,7 +87,7 @@ public override bool RowUpdatePossible
 			get { return false; }
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			var entityMode = Session.EntityMode;
 			var clonedSet = new SetSnapShot<T>(set.Count);

src/NHibernate/Collection/IPersistentCollection.cs

@@ -251,7 +251,7 @@ public interface IPersistentCollection
 		/// <summary>
 		/// Return a new snapshot of the current state of the collection
 		/// </summary>
-		ICollection GetSnapshot(ICollectionPersister persister);
+		object GetSnapshot(ICollectionPersister persister);
 
 		/// <summary>
 		/// To be called internally by the session, forcing

src/NHibernate/Collection/PersistentArrayHolder.cs

@@ -67,7 +67,7 @@ public override object GetValue()
 			return array;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 

src/NHibernate/Collection/PersistentBag.cs

@@ -132,7 +132,7 @@ private static int CountOccurrences(object element, IList list, IType elementTyp
 			return result;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 			List<object> clonedList = new List<object>(bag.Count);

src/NHibernate/Collection/PersistentIdentifierBag.cs

@@ -196,7 +196,7 @@ public override bool EqualsSnapshot(ICollectionPersister persister)
 
 		public override bool IsSnapshotEmpty(object snapshot)
 		{
-			return ((ICollection) snapshot).Count == 0;
+			return ((ISet<SnapshotElement>) snapshot).Count == 0;
 		}
 
 		public override IEnumerable GetDeletes(ICollectionPersister persister, bool indexIsFormula)
@@ -271,7 +271,7 @@ public override object ReadFrom(IDataReader reader, ICollectionPersister persist
 			return element;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 

src/NHibernate/Collection/PersistentList.cs

@@ -51,7 +51,7 @@ public PersistentList(ISessionImplementor session, IList list) : base(session)
 			IsDirectlyAccessible = true;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 

src/NHibernate/Collection/PersistentMap.cs

@@ -42,7 +42,7 @@ public PersistentMap(ISessionImplementor session, IDictionary map) : base(sessio
 			IsDirectlyAccessible = true;
 		}
 
-		public override ICollection GetSnapshot(ICollectionPersister persister)
+		public override object GetSnapshot(ICollectionPersister persister)
 		{
 			EntityMode entityMode = Session.EntityMode;
 			Hashtable clonedMap = new Hashtable(map.Count);