Zero-length arrays

In C++ codebases that are written in a C style or that make use of C libraries, null pointers may be used to represent empty arrays.

In Rust, arrays of arbitrary size are represented as slices. These slices can have zero length. Since Rust vectors are convertible to slices, defining functions that work with slices enables them to be used with vectors as well.

#include <cstddef>
#include <cassert>

int c_style_sum(std::size_t len, int arr[]) {
    int sum = 0;
    for (size_t i = 0; i < len; i++) {
        sum += arr[i];
    }
    return sum;
}

int main() {
    int sum = c_style_sum(0, nullptr);
    assert(sum == 0);
}

fn sum_slice(arr: &[i32]) -> i32 {
    let mut sum = 0;
    for x in arr {
        sum += x;
    }
    sum
}

fn main() {
    let sum = sum_slice(&[]);
    assert!(sum == 0);

    let sum2 = sum_slice(&vec![]);
    assert!(sum2 == 0);
}