// *** before: ***
extern "C" {
fn abs(input: i32) -> i32;
}
// *** in version Rust 2024: ***
// declaring a foreign function is a promise to the compiler, and unsafe
unsafe extern "C" {
fn abs(input: i32) -> i32; // call it inside unsafe only
safe fn sqrt(x: f64) -> f64; // and this one is marked safe
}