/** * Binds variables for use in the specified expression, and returns the * result of the expression. * * @see http://docs.mongodb.org/manual/reference/operator/aggregation/let/ * @see Expr::let * @param mixed|Expr $vars Assignment block for the variables accessible in the in expression. To assign a variable, specify a string for the variable name and assign a valid expression for the value. * @param mixed|Expr $in The expression to evaluate. * @return self */ public function let($vars, $in) { $this->expr->let($vars, $in); return $this; }