Trait Bounds

When working with generics, you often want to require the types to implement some trait, so that you can call this trait's methods.

You can do this with T: Trait:

fn duplicate<T: Clone>(a: T) -> (T, T) {
    (a.clone(), a.clone())
}

// struct NotCloneable;

fn main() {
    let foo = String::from("foo");
    let pair = duplicate(foo);
    println!("{pair:?}");
}

This slide should take about 8 minutes.

Try making a NonCloneable and passing it to duplicate.
When multiple traits are necessary, use + to join them.
Show a where clause, students will encounter it when reading code.
```
fn duplicate<T>(a: T) -> (T, T)
where
    T: Clone,
{
    (a.clone(), a.clone())
}
```
- It declutters the function signature if you have many parameters.
- It has additional features making it more powerful.
  - If someone asks, the extra feature is that the type on the left of ":" can be arbitrary, like Option<T>.
Note that Rust does not (yet) support specialization. For example, given the original duplicate, it is invalid to add a specialized duplicate(a: u32).

Comprehensive Rust 🦀

Trait Bounds