Option - Rust By Example
Description: Rust by Example (RBE) is a collection of runnable examples that illustrate various Rust concepts and standard libraries.

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# `Option`

Sometimes it’s desirable to catch the failure of some parts of a program instead of calling `panic!`; this can be accomplished using the `Option` enum.

The `Option<T>` enum has two variants:

- `None`, to indicate failure or lack of value, and
- `Some(value)`, a tuple struct that wraps a `value` with type `T`.

    // An integer division that doesn't `panic!`
    fn checked_division(dividend: i32, divisor: i32) -> Option<i32> {
        if divisor == 0 {
            // Failure is represented as the `None` variant
            None
        } else {
            // Result is wrapped in a `Some` variant
            Some(dividend / divisor)
        }
    }

    // This function handles a division that may not succeed
    fn try_division(dividend: i32, divisor: i32) {
        // `Option` values can be pattern matched, just like other enums
        match checked_division(dividend, divisor) {
            None => println!("{} / {} failed!", dividend, divisor),
            Some(quotient) => {
                println!("{} / {} = {}", dividend, divisor, quotient)
            },
        }
    }

    fn main() {
        try_division(4, 2);
        try_division(1, 0);

        // Binding `None` to a variable needs to be type annotated
        let none: Option<i32> = None;
        let _equivalent_none = None::<i32>;

        let optional_float = Some(0f32);

        // Unwrapping a `Some` variant will extract the value wrapped.
        println!("{:?} unwraps to {:?}", optional_float, optional_float.unwrap());

        // Unwrapping a `None` variant will `panic!`
        println!("{:?} unwraps to {:?}", none, none.unwrap());
    }