Function borrow_as_box

pub fn borrow_as_box<T: Default, R, F: FnOnce(Box<T>) -> (R, Box<T>)>(
    ptr: &mut T,
    f: F,
) -> R

Borrows a mutable reference as Box for the lifespan of this function. Runs the given closure with the boxed value as a parameter. The closure is expected to return a boxed value, whose changes will be reflected on the mutable reference. Example:

use cairo_lang_utils::borrow_as_box;
let mut x = 5;
borrow_as_box(&mut x, |mut x: Box<usize>| {
    *x += 1;
    ((), x)
});
assert_eq!(x, 6);