4. Strings and String Slices

strings.md

4. Strings and String Slices

• String vs. &String vs. &str vs. str
• String constants
• Converting between strings and slices
• Taking a slice of a string
• Byte slices
• Conversion to strings
• Unsafe but fast
• Function arguments: prefer &str over &String

String vs. &str and byte sizes

fn main() {
    let s : String = "abc".to_string();
    let t : &str = "xyz";
    println!("{} {} {} {}",
             s, std::mem::size_of::<String>(),
             t, std::mem::size_of::<&str>());
    println!("{}", std::mem::size_of::<&mut String>());
}

Converting between String and &str

fn main() {
    let s : String = "abc".to_string();
    let t = &s[1..2];
    println!("{} {} {} {}",
             s, std::mem::size_of::<String>(),
             t, std::mem::size_of::<&str>());
}

Byte slices

fn main() {
    let s : String = "abc".to_string();
    let t = &s[1..2];
    let b = std::str::from_utf8(b"pqr").unwrap();
    println!("{} {} {} {} {}",
             s, std::mem::size_of::<String>(),
             t, std::mem::size_of::<&str>(), b);
}

Unsafe

fn main() {
    let s : String = "abc".to_string();
    let t = &s[1..2];
    let b = unsafe {
        std::str::from_utf8_unchecked(b"pqr")
    };
    println!("{} {} {} {} {}",
             s, std::mem::size_of::<String>(),
             t, std::mem::size_of::<&str>(), b);
}

Function arguments

fn f(s : &str) {
    println!("In f: {}", s);
}

fn main() {
    let s : String = "abc".to_string();
    f(&s);
    let t = &s[1..2];
    f(t);
    println!("{} {} {} {}",
             s, std::mem::size_of::<String>(),
             t, std::mem::size_of::<&str>());
}

References:

• Rust book: https://doc.rust-lang.org/book/ch08-02-strings.html
• Video: https://youtu.be/fMt7Xi4BfZU
• Overview: https://gist.github.com/max-itzpapalotl/18f7675a60f6f9603250367bcb63992e