rust - String and str

main.rs

fn main() {
    
    let mut txt = "Hello, World!".to_string(); // txt: String
    println!("first its: {}", txt);

    txt = get_pling(txt); 
    println!("then its: {}",txt);

    add_in_place_plong(&mut txt); // passes a mutable reference
    println!("finally its: {}", txt);
    
    let y = txt.as_slice(); // y: &str
    print_foo(y); // borrow y to print_foo
    println!("still here: {}", y);

    let z = box y;  // copy 
    say_foobar(z);  // passed ownership forward

    // would error cause ownership moved
    //println!("errors: {}", z);
    println!("works: {}", y);

}

// copies given string modfies and returns
fn get_pling(arg: String) -> String {
    let mut ret = arg;
    ret.push_str("\n about 42");
    ret.to_string()
}

// modifies given reference
fn add_in_place_plong(arg: &mut String) {
    arg.push_str("\n working...");
}

// borrow arg
fn print_foo(arg: &str) {
    println!("summed up: {}", arg);
}

// becomes owner
fn say_foobar(arg: Box<&str>) {
    println!("saying: {}", *arg);
}