16.4 Generic function

Here is an example of a generic function. It takes a single parameter T and uses it to define the type of its single argument:

fn get_length<T>(v: &[T]) -> usize {
  v.len()
}

let arr = [16, -10, 120];
get_length(&arr)

The previous function does not do anything useful, and thus does not put any constraint on the type T. Usually, we use T inside the function’s code, like calling one of its methods or using an operator on it. This implies that T must provide some abilities. The following example needs the T type to be compared using the > operator. This implies that T must implement the PartialOrd trait. The function returns the highest element in an array of any type T:

:clear

use std::cmp::PartialOrd;

fn largest<T: PartialOrd>(arr: &[T]) -> &T {
  let mut largest = &arr[0];

  for item in arr {
    if item > largest {
      largest = item;
    }
  }

  largest
}

We apply the function first on a list of integers:

{
  let number_list = vec![34, 50, 25, 100, 65];
  let result = largest(&number_list);
  println!("The largest number is {result}");
}

The largest number is 100

Now we apply it on a list of characters:

{
  let char_list = vec!['y', 'm', 'a', 'q'];
  let result = largest(&char_list);
  println!("The largest char is {result}");
}

The largest char is y

see solution