use std::ops::Range;

fn map_mut<T, F>(arr: &mut [T], range: Range<usize>, f: F)
where
    F: Fn(&T) -> T
{
    let slice = arr[range].iter_mut();

    for element in slice {
        *element = f(element);
    }
}


fn magic(_: &i32) -> i32 { 42 }


fn main() {
    let mut arr = vec![1, 2, 3, 4];

    map_mut(&mut arr, 1..3, magic);
    map_mut(&mut arr, 1..3, |x| x * 10);

    println!("{:?}", arr);
}