Derive - Rust By Example
Description: A description

# 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 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`