ToString and FromStr trait: To and from Strings

ToString from Display: 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());
}

FromStr: 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.

fn main() {
    let parsed: i32 = "5".parse().unwrap();
    let turbo_parsed = "10".parse::<i32>().unwrap();

    let sum = parsed + turbo_parsed;
    println!("Sum: {:?}", sum);
}

• This will convert the string into the type specified as 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.