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

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minutes: 10
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<!-- NOTES:
Tuple structs, newtype wrappers, unit-like structs, including initialization syntax
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# Tuple Structs

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

```rust,editable
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):

```rust,editable,compile_fail
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);
}
```

<details>

- 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)`.
- Demonstrate how to add a `f64` value to a `Newtons` type by accessing the
  single field in the newtype.
  - Rust generally doesn’t like inexplicit things, like automatic unwrapping or
    for instance using booleans as integers.
  - Operator overloading is discussed on Day 3 (generics).
- The example is a subtle reference to the
  [Mars Climate Orbiter](https://en.wikipedia.org/wiki/Mars_Climate_Orbiter)
  failure.

</details>