/**
* 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;
}
