TryFrom and TryInto - 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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# `TryFrom` and `TryInto`

Similar to `From` and `Into`, `TryFrom` and `TryInto` are generic traits for converting between types. Unlike `From`/`Into`, the `TryFrom`/`TryInto` traits are used for fallible conversions, and as such, return `Result`s.

    use std::convert::TryFrom;
    use std::convert::TryInto;

    #[derive(Debug, PartialEq)]
    struct EvenNumber(i32);

    impl TryFrom<i32> for EvenNumber {
        type Error = ();

        fn try_from(value: i32) -> Result<Self, Self::Error> {
            if value % 2 == 0 {
                Ok(EvenNumber(value))
            } else {
                Err(())
            }
        }
    }

    fn main() {
        // TryFrom

        assert_eq!(EvenNumber::try_from(8), Ok(EvenNumber(8)));
        assert_eq!(EvenNumber::try_from(5), Err(()));

        // TryInto

        let result: Result<EvenNumber, ()> = 8i32.try_into();
        assert_eq!(result, Ok(EvenNumber(8)));
        let result: Result<EvenNumber, ()> = 5i32.try_into();
        assert_eq!(result, Err(()));
    }