TryFrom and TryInto

Introduction

In this lab, we explore the usage of TryFrom and TryInto in Rust, which are generic traits used for fallible conversions between types and return Result types. We provide an example code snippet that demonstrates the implementation of TryFrom for converting an i32 into a custom EvenNumber struct, and then showcase how to use TryFrom and TryInto to perform the conversion and handle the possible errors.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

Skills Graph

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(()));
}

Summary

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