(stdDevPopField: StringAdd).self
(stdDevPopField: StringFormat).self
(stdDevPopField: ArrowAssoc[AggregationFramework.StdDevPopField]).x
(Since version 2.10.0) Use leftOfArrow
instead
(stdDevPopField: Ensuring[AggregationFramework.StdDevPopField]).x
(Since version 2.10.0) Use resultOfEnsuring
instead
The $stdDevPop for a single field (since MongoDB 3.2)