comprehensive-rust/src/user-defined-types/tuple-structs.md

minutes

minutes
10

Tuple Structs

If the field names are unimportant, you can use a tuple struct:

struct Point(i32, i32);

fn main() {
    let p = Point(17, 23);
    println!("({}, {})", p.0, p.1);
}

This is often used for single-field wrappers (called newtypes):

struct PoundsOfForce(f64);
struct Newtons(f64);

fn compute_thruster_force() -> PoundsOfForce {
    todo!("Ask a rocket scientist at NASA")
}

fn set_thruster_force(force: Newtons) {
    // ...
}

fn main() {
    let force = compute_thruster_force();
    set_thruster_force(force);
}

• Newtypes are a great way to encode additional information about the value in a primitive type, for example:
  • The number is measured in some units: Newtons in the example above.
  • The value passed some validation when it was created, so you no longer have to validate it again at every use: PhoneNumber(String) or OddNumber(u32).
• The newtype pattern is covered extensively in the "Idiomatic Rust" module.
• Demonstrate how to add a f64 value to a Newtons type by accessing the single field in the newtype.
  • Rust generally avoids implicit conversions, like automatic unwrapping or using booleans as integers.
    • Operator overloading is discussed on Day 2 (Standard Library Traits).
• When a tuple struct has zero fields, the () can be omitted. The result is a zero-sized type (ZST), of which there is only one value (the name of the type).
  • This is common for types that implement some behavior but have no data (imagine a NullReader that implements some reader behavior by always returning EOF).
• The example is a subtle reference to the Mars Climate Orbiter failure.