(stdDevPop: StringAdd).self
(stdDevPop: StringFormat).self
(stdDevPop: ArrowAssoc[AggregationFramework.StdDevPop]).x
(Since version 2.10.0) Use leftOfArrow
instead
(stdDevPop: Ensuring[AggregationFramework.StdDevPop]).x
(Since version 2.10.0) Use resultOfEnsuring
instead
The $stdDevPop group accumulator (since MongoDB 3.2)