The bug Rust won't let you write

fn describe(name: String) -> String {
    format!("hi {name}")
}

fn main() {
    let name = String::from("hello");
    let msg = describe(name); // ownership moves into describe

    // let n = name.len();    // <- uncomment: error[E0382]
    //                        // borrow of moved value: `name`

    // Fix A: read the length BEFORE moving.
    let a = String::from("world");
    let n = a.len();          // borrow, a still owned
    let msg2 = describe(a);   // now move it

    println!("{msg} / {msg2} / len was {n}");
}

fn describe(name: String) -> String {
    format!("hi {name}")
}

fn main() {
    let name = String::from("hello");
    let msg = describe(name.clone()); // give describe its OWN copy
    let n = name.len();               // original still owned here

    println!("{msg}, and name is still {n} bytes: {name}");
}

fn main() {
    let mut v = vec![10, 20, 30];

    // let first = &v[0];  // a reference INTO v
    // v.push(40);         // <- error[E0502]: may reallocate,
    //                     //    first would dangle
    // println!("{first}");

    // The safe shape: finish reading, THEN mutate.
    let first = v[0];      // copy the i32 out (i32 is Copy)
    v.push(40);
    println!("first was {first}, v is now {v:?}");
}