Rust Trait (1): AsRef, AsMut

// Obtain the number of bytes (not characters) in the given argument.
fn byte_counter<T>(arg: T) -> usize where T: AsRef<str> {
    arg.as_ref().as_bytes().len()
}

// Obtain the number of characters (not bytes) in the given argument.
fn char_counter<T>(arg: T) -> usize where T: AsRef<str> {
    arg.as_ref().chars().count()
}

// =================
// ===== TESTS =====
// =================
#[test]
fn different_counts() {
    let s = "Café au lait";
    assert_ne!(char_counter(s), byte_counter(s));
}

#[test]
fn same_counts() {
    let s = "Cafe au lait";
    assert_eq!(char_counter(s), byte_counter(s));
}

#[test]
fn different_counts_using_string() {
    let s = String::from("Café au lait");
    assert_ne!(char_counter(s.clone()), byte_counter(s));
}

#[test]
fn same_counts_using_string() {
    let s = String::from("Cafe au lait");
    assert_eq!(char_counter(s.clone()), byte_counter(s));
}

// Squares a number using as_mut().
fn num_sq<T>(arg: &mut T) where T: AsMut<u32> {
    let value = arg.as_mut();
    *value *= *value;
}

// =================
// ===== TESTS =====
// =================
#[test]
fn mult_box() {
    let mut num: Box<u32> = Box::new(3);
    num_sq(&mut num);
    assert_eq!(*num, 9);
}