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.

Comprehensive Rust 🦀

Strings