public static Task<long> CountAsync<TDocument>(
	this IMongoCollection<TDocument> collection,
	Expression<Func<TDocument, bool>> filter,
	CountOptions options = null,
	CancellationToken cancellationToken = null
)

<ExtensionAttribute>
Public Shared Function CountAsync(Of TDocument) ( 
	collection As IMongoCollection(Of TDocument),
	filter As Expression(Of Func(Of TDocument, Boolean)),
	Optional options As CountOptions = Nothing,
	Optional cancellationToken As CancellationToken = Nothing
) As Task(Of Long)

[<ExtensionAttribute>]
static member CountAsync : 
        collection : IMongoCollection<'TDocument> * 
        filter : Expression<Func<'TDocument, bool>> * 
        ?options : CountOptions * 
        ?cancellationToken : CancellationToken 
(* Defaults:
        let _options = defaultArg options null
        let _cancellationToken = defaultArg cancellationToken null
*)
-> Task<int64>