rust example for ? operator

 This is an example of using Result and operator ? in Rust. 

Let's say I have the following division function 

fn div(self, x: f64, y: f64) -> MathResult {

        if y == 0.0 {

            Err(MathError::DivisionByZero)

        } else {

            Ok(x / y)

        }

    }

When i call using the code here, it says "the `?` operator can only be used in a method that returns `Result` or `Option"

fn op1(self, x: f64, y: f64) {

        // if `div` "fails", then `DivisionByZero` will be `return`ed

        let ratio = self.div(x, y)?;

        Ok(10.0)

    }

Rightly pointed out so, if i change my function to this (that returns MathResult), then i was able to use the ? operator.

fn op2(self, x: f64, y: f64) -> MathResult {

        // if `div` "fails", then `DivisionByZero` will be `return`ed

        let ratio = self.div(x, y)?;

        Ok(10.0)

    }

Given that we expect that an error could occur and therefore handle it, we need to have this "handler" somewhere up the call stacks.