Package accumulators provides aggregation accumulator operators.

IsOperator returns true if provided document should be treated as operator document.

NewExpr validates and creates $expr operator which allows usage of aggregation expression from query and $match aggregation stage.

NewOperator returns operator from provided document.

ErrArgsInvalidLen indicates that operator have invalid amount of arguments.

ErrInvalidExpression indicates that given operator does not exist.

ErrInvalidNestedExpression indicates that operator inside the target operator does not exist.

ErrNotImplemented indicates that given operator is not implemented yet.

ErrTooManyFields indicates that operator field specifes more than one operators.

Operators maps all standard aggregation operators.

OperatorError is used for reporting operator errors.

Operator is a common interface for standard aggregation operators.