Rust by Example

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 Results.

use std::convert::TryFrom;

use std::convert::TryInto;

#[derive(Debug, PartialEq)]

struct EvenNumber(i32);

impl TryFrom for EvenNumber {

type Error = ();

fn try_from(value: i32) -> Result {

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 = 8i32.try_into();

assert_eq!(result, Ok(EvenNumber(8)));

let result: Result = 5i32.try_into();

assert_eq!(result, Err(()));

}

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To and from Strings

Converting to String

To convert any type to a String is as simple as implementing the ToString trait for the type. Rather than doing so directly, you should implement the fmt::Display trait which automagically provides ToString and also allows printing the type as discussed in the section on print!.

use std::fmt;

struct Circle {

radius: i32

}

impl fmt::Display for Circle {

fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

write!(f, "Circle of radius {}", self.radius)

}

}

fn main() {

let circle = Circle { radius: 6 };

println!("{}", circle.to_string());

}

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Parsing a String

One of the more common types to convert a string into is a number. The idiomatic approach to this is to use the parse function and either to arrange for type inference or to specify the type to parse using the 'turbofish' syntax. Both alternatives are shown in the following example.

This will convert the string into the type specified so long as the FromStr trait is implemented for that type. This is implemented for numerous types within the standard library. To obtain this functionality on a user defined type simply implement the FromStr trait for that type.

fn main() {

let parsed: i32 = "5".parse().unwrap();

let turbo_parsed = "10".parse::().unwrap();