use std::borrow::Cow;

fn foo<'a, T: Into<Cow<'a, str>>>(arg: T) {
    let owned: String = match arg.into() {
        Cow::Borrowed(string) => {
            println!("allocates");
            string.to_owned()
        },
        Cow::Owned(string) => {
            println!("doesn't allocate");
            string
        },
    };

    println!("{}", owned);
}


fn main() {
    let borrowed: &str = "test1";
    foo(borrowed);
    let owned: String = "test2".into();
    foo(owned);
}