use std::borrow::Cow;

fn ensure_owned(s: Cow<str>) -> String {
    // only clones if borrowed
    s.into_owned()
}

fn process(input: &str) -> Cow<str> {
    if input.contains("bad") {
        Cow::Owned(input.replace("bad", "good"))
    } else {
        Cow::Borrowed(input)
    }
}

fn main() {
    // borrowed case: no allocation
    let s1 = process("hello world");
    println!("{:?}", s1);

    // owned case: new allocation
    let s2 = process("bad word");
    println!("{:?}", s2);

    // Cow with Vec
    let v = vec![1, 2, 3];
    let cow: Cow<[i32]> = Cow::Borrowed(&v);
    println!("borrowed: {:?}", cow);
}