Strings

String type

fn main() {
    // `String` is Unicode, not ASCII
    let mut s1 = String::from("hello");
    s1.push_str(", world!"); // `String` can be mutated
    s1.clear(); // Empties the String, making it equal to ""

    // Alternative initialization from string literals
    // `to_string` is available on any type that implements
    // the Display trait
    let s2 = "initial contents".to_string();

    // Concatenation: note s1 has been moved here and can no longer
    // be used afterwards
    let s3 = s1 + &s2;
    // ERROR let s = format!("{s1}-{s2}-{s3}");

    // String slice -  contains the first 4 bytes of the string.
    let _s: &str = &s3[0..4];
    // Caution: If we were to try to slice only part of a unicode
    // character’s bytes, Rust would panic at runtime.

    // Iteration
    for c in "Зд".chars() {
        println!("{c}");
    }
    for b in "Зд".bytes() {
        println!("{b}");
    }
}

Placeholders

fn main() {
    let x = 5;
    let y = 10;

    println!("x = {x} and y + 2 = {}", y + 2);
}

Use {:?} to use the Debug output format (annotate type with #[derive(Debug)]) or {:#?} for pretty print.

Also use dbg!(&rect1); for debug output (returns ownership of the expression’s value).

String concatenation

Here are several common methods to concatenate Strings:

#![allow(clippy::vec_init_then_push)]

#[macro_use(concat_string)]
extern crate concat_string;

#[macro_use(concat_strs)]
extern crate concat_strs;

static DATE: &str = "2024-01-15";
static T: &str = "T";
static TIME: &str = "12:00:09Z";

fn main() {
    let _datetime = &[DATE, T, TIME].concat();

    let _datetime = &[DATE, TIME].join(T);

    let _datetime = &[DATE, T, TIME].join("");

    let _datetime = &[DATE, T, TIME].join("");

    let list = [DATE, T, TIME];
    // let _datetime: String = list.iter().map(|x| *x).collect();
    let _datetime: String = list.iter().copied().collect();

    #[allow(clippy::useless_vec)]
    let list = vec![DATE, T, TIME];
    // let _datetime: String = list.iter().map(|x| *x).collect();
    let _datetime: String = list.iter().copied().collect();

    let _datetime = &format!("{}{}{}", DATE, T, TIME);

    let _datetime = &format!("{DATE}{T}{TIME}");

    let mut datetime = String::new();
    datetime.push_str(DATE);
    datetime.push_str(T);
    datetime.push_str(TIME);

    let mut datetime = Vec::<String>::new();
    datetime.push(String::from(DATE));
    datetime.push(String::from(T));
    datetime.push(String::from(TIME));
    let _datetime = datetime.join("");

    let mut datetime = String::with_capacity(20);
    datetime.push_str(DATE);
    datetime.push_str(T); // or 'T'
    datetime.push_str(TIME);

    let _datetime =
        &(String::from(DATE) + &String::from(T) + &String::from(TIME));

    let _datetime = &(String::from(DATE) + T + TIME);

    let _datetime = &(DATE.to_owned() + T + TIME);

    let _datetime = &(DATE.to_string() + T + TIME);

    let _datetime = concat_string!(DATE, T, TIME);

    let _datetime = &concat_strs!(DATE, T, TIME);
}

Examples from concatenation_benchmarks-rs