Code review changes.

Author: rstam

MongoDB.Driver/AggregateArgs.cs

@@ -114,26 +114,7 @@ public AggregateOutputMode OutputMode
         public IEnumerable<BsonDocument> Pipeline
         {
             get { return _pipeline; }
-            set { _pipeline = value; }
-        }
-
-        // internal methods
-        internal AggregateArgs WithMaterializedPipeline()
-        {
-            if (_pipeline is BsonDocument[] || _pipeline is List<BsonDocument>)
-            {
-                return this;
-            }
-
-            var materializedPipeline = _pipeline.ToArray();
-            return new AggregateArgs
-            {
-                AllowDiskUse = _allowDiskUse,
-                BatchSize = _batchSize,
-                MaxTime = _maxTime,
-                OutputMode = _outputMode,
-                Pipeline = materializedPipeline
-            };
+            set { _pipeline = value.ToList(); }
         }
     }
 }

MongoDB.Driver/MongoCollection.cs

@@ -125,7 +125,6 @@ public virtual IEnumerable<BsonDocument> Aggregate(AggregateArgs args)
             if (args == null) { throw new ArgumentNullException("args"); }
             if (args.Pipeline == null) { throw new ArgumentException("Pipeline is null.", "args"); }
 
-            args = args.WithMaterializedPipeline(); // materialize the pipeline if necessary to prevent double enumeration side effects
             var lastStage = args.Pipeline.LastOrDefault();
 
             string outputCollectionName = null;
@@ -1725,7 +1724,7 @@ public ReadOnlyCollection<IEnumerator> ParallelScanAs(Type documentType, Paralle
             var methodInfo = methodDefinition.MakeGenericMethod(documentType);
             try
             {
-                return new ReadOnlyCollection<IEnumerator>(((IEnumerable)methodInfo.Invoke(this, new object[] { args })).Cast<IEnumerator>().ToList());
+                return ((IEnumerable)methodInfo.Invoke(this, new object[] { args })).Cast<IEnumerator>().ToList().AsReadOnly();
             }
             catch (TargetInvocationException ex)
             {

MongoDB.Driver/Operations/ParallelScanOperation.cs

@@ -114,7 +114,7 @@ public ReadOnlyCollection<IEnumerator<TDocument>> Execute(MongoConnection connec
                 enumerators.Add(enumerator);
             }
 
-            return new ReadOnlyCollection<IEnumerator<TDocument>>(enumerators);
+            return enumerators.AsReadOnly();
         }
     }
 }