Tuple Structs

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

// Copyright 2023 Google LLC
// SPDX-License-Identifier: Apache-2.0

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):

// Copyright 2023 Google LLC
// SPDX-License-Identifier: Apache-2.0

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);
}

This slide should take about 10 minutes.

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.

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Tuple Structs