Derive

The compiler is capable of providing basic implementations for some traits via the #[derive] attribute. These traits can still be manually implemented if a more complex behavior is required.

The following is a list of derivable traits:

• Comparison traits: Eq, PartialEq, Ord, PartialOrd.
• Clone, to create T from &T via a copy.
• Copy, to give a type 'copy semantics' instead of 'move semantics'.
• Hash, to compute a hash from &T.
• Default, to create an empty instance of a data type.
• Debug, to format a value using the {:?} formatter.

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// `Centimeters`, a tuple struct that can be compared
#[derive(PartialEq, PartialOrd)]
struct Centimeters(f64);
// `Inches`, a tuple struct that can be printed
#[derive(Debug)]
struct Inches(i32);
impl Inches {
    fn to_centimeters(&self) -> Centimeters {
        let &Inches(inches) = self;
        Centimeters(inches as f64 * 2.54)
    }
}
// `Seconds`, a tuple struct with no additional attributes
struct Seconds(i32);
fn main() {
    let _one_second = Seconds(1);
    // Error: `Seconds` can't be printed; it doesn't implement the `Debug` trait
    //println!("One second looks like: {:?}", _one_second);
    // TODO ^ Try uncommenting this line
    // Error: `Seconds` can't be compared; it doesn't implement the `PartialEq` trait
    //let _this_is_true = (_one_second == _one_second);
    // TODO ^ Try uncommenting this line
    let foot = Inches(12);
    println!("One foot equals {:?}", foot);
    let meter = Centimeters(100.0);
    let cmp =
        if foot.to_centimeters() < meter {
            "smaller"
        } else {
            "bigger"
        };
    println!("One foot is {} than one meter.", cmp);
}
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See also:

derive