Derive Traits in Rust Tuple Structs

Introduction

In this lab, we learn about the #[derive] attribute in Rust, which allows the compiler to provide basic implementations for certain traits such as Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Hash, Default, and Debug. These traits can also be manually implemented if a more complex behavior is needed. The lab provides example code showcasing the usage of these traits on different tuple structs such as Centimeters, Inches, and Seconds.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

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);
}

Summary

Congratulations! You have completed the Derive lab. You can practice more labs in LabEx to improve your skills.