Use the Debug Formatter

Rust's standard library types are all printable using the debug formatter {:?} or the "pretty printing" formatter {:#?}.

fn main() {
    let vec = vec![0, 1, 2, 3];

    println!("Debug: {:?}", vec);
    println!("Pretty print: {:#?}", vec);
}

In contrast, the default formatter throws an error.

fn main() {
    let vec = vec![0, 1, 2, 3];

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