Printing with Derived Traits

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

fn main() {
    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };

    println!("rect1 is {:?}", rect1);
}

Putting the specifier :? inside the curly brackets tells println! we want to use an output format called Debug. The Debug trait enables us to print our struct in a way that is useful for developers so we can see its value while we’re debugging our code.

Rust does include functionality to print out debugging information, but we have to explicitly opt in to make that functionality available for our struct. To do that, we add the outer attribute #[derive(Debug)] just before the struct definition,

To format the output we use {:#?}