Strings

Rust has two types to represent strings, both of which will be covered in more depth later. Both always store UTF-8 encoded strings.

  • String - a modifiable, owned string.
  • &str - a read-only string. String literals have this type.
fn main() {
    let greeting: &str = "Greetings";
    let planet: &str = "🪐";
    let mut sentence = String::new();
    sentence.push_str(greeting);
    sentence.push_str(", ");
    sentence.push_str(planet);
    println!("final sentence: {}", sentence);
    println!("{:?}", &sentence[0..5]);
    //println!("{:?}", &sentence[12..13]);
}
This slide should take about 5 minutes.

This slide introduces strings. Everything here will be covered in more depth later, but this is enough for subsequent slides and exercises to use strings.

  • Invalid UTF-8 in a string is UB, and this not allowed in safe Rust.

  • String is a user-defined type with a constructor (::new()) and methods like s.push_str(..).

  • The & in &str indicates that this is a reference. We will cover references later, so for now just think of &str as a unit meaning “a read-only string”.

  • The commented-out line is indexing into the string by byte position. 12..13 does not end on a character boundary, so the program panics. Adjust it to a range that does, based on the error message.

  • Raw strings allow you to create a &str value with escapes disabled: r"\n" == "\\n". You can embed double-quotes by using an equal amount of # on either side of the quotes:

    fn main() {
        println!(r#"<a href="link.html">link</a>"#);
        println!("<a href=\"link.html\">link</a>");
    }
  • Using {:?} is a convenient way to print array/vector/struct of values for debugging purposes, and it’s commonly used in code.