<ExtensionAttribute()>
Public Overloads Shared Function Sum(Of TSource)( _
   ByVal source As IEntityScalarQuery(Of TSource), _
   Optional ByVal userCallback As Action(Of EntityScalarQueryOperation(Of TSource)), _
   Optional ByVal userState As Object _
) As EntityScalarQueryOperation(Of TSource)

Dim source As IEntityScalarQuery(Of TSource)
Dim userCallback As Action(Of EntityScalarQueryOperation(Of TSource))
Dim userState As Object
Dim value As EntityScalarQueryOperation(Of TSource)
 
value = EntityScalarAsyncExtensions.Sum(Of TSource)(source, userCallback, userState)

[ExtensionAttribute()]
public static EntityScalarQueryOperation<TSource> Sum<TSource>( 
   IEntityScalarQuery<TSource> source,
   Action<EntityScalarQueryOperation<TSource>> userCallback,
   object userState
)

[ExtensionAttribute()]
public:
static EntityScalarQueryOperation<TSource^>^ Sumgeneric<typename TSource>
( 
   IEntityScalarQuery<TSource^>^ source,
   Action<EntityScalarQueryOperation<TSource^>^>^ userCallback,
   Object^ userState
) 

public void AsyncSum() {
   var op = _entityManager.OrderSummaries.Select(o => o.Freight).AsScalarAsync().Sum();
   op.Completed += (o, e) => {
     var ct = e.Result;
   };
 }