Generics

Generics are a way to make a function or a type work for multiple types to avoid code duplication. Let's rewrite our max function to make it generic:

fn max<T: PartialOrd>(a: T, b: T) -> T {
    if a > b {
        a
    } else {
        b
    }
}

The first thing to note is that there's a new part after the function name: this is where we declare the generic types. We declare a generic T type, : PartialOrd after it means that this T type must implement the PartialOrd trait. This is called a trait bound. We then use this T type for both of our parameters and the return type. Then, we see the same function body as the one from our non-generic function. We needed to add the trait bound because, by default, no operation is allowed on a generic type. The PartialOrd trait allows us to use the comparison operators.

We can then use this function with any type that implements PartialOrd:

println!("{}", max('a', 'z'));

This is using static dispatch as opposed to dynamic dispatch, meaning that the compiler will generate a max function specific to char in the resulting binary. Dynamic dispatch is another approach that resolves the right function to call at runtime, which is less efficient.