use std::cell::RefCell;

struct Foo<'a> {
    x: RefCell<Option<&'a mut [u8]>>
}

impl<'a> Foo<'a> {
    fn set(&self, arr: &'a mut [u8]) {
        *self.x.borrow_mut() = Some(arr);
    }

    fn remove(&self) -> &'a mut [u8] {
        self.x.borrow_mut().take().unwrap()
    }

}

pub fn main(){
    let foo = Foo {x: RefCell::new(None)};
    let mut arr = Vec::with_capacity(100).into_boxed_slice();

    {
        foo.set(&mut arr);


        foo.get();

    }

}