public static Task<double> SumAsync<TSource>(
	this IQueryable<TSource> source,
	Expression<Func<TSource, double>> selector,
	CancellationToken cancellationToken
)

<ExtensionAttribute>
Public Shared Function SumAsync(Of TSource) ( 
	source As IQueryable(Of TSource),
	selector As Expression(Of Func(Of TSource, Double)),
	cancellationToken As CancellationToken
) As Task(Of Double)