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.

// `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);
}

See also:

derive