Debug

“Write to string” trait, for debug purposes.

Derivable: ✅

When to implement: Almost always

// pub trait Debug {
//     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>;
// }

#[derive(Debug)]
pub struct Date {
    day: u8,
    month: u8,
    year: i64,
}

#[derive(Debug)]
pub struct User {
    name: String,
    date_of_birth: Date,
}

pub struct PlainTextPassword {
    password: String,
    hint: String,
}

impl std::fmt::Debug for PlainTextPassword {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("PlainTextPassword")
            .field("hint", &self.hint)
            .field("password", &"[omitted]")
            .finish()
    }
}

fn main() {
    let user = User {
        name: "Alice".to_string(),
        date_of_birth: Date { day: 31, month: 10, year: 2002 },
    };

    println!("{user:?}");
    println!(
        "{:?}",
        PlainTextPassword {
            password: "Password123".to_string(),
            hint: "Used it for years".to_string()
        }
    );
}