use std::ops::{Deref, DerefMut};

pub struct DynBorrower<'a, T: ?Sized> {
    data: &'a mut T,
    borrowed: &'a mut bool,
}

impl<'a, T: ?Sized> DynBorrower<'a, T> {
    pub fn new(data: &'a mut T, borrowed: &'a mut bool) -> Self {
        if *borrowed {
            panic!("tried to mutably borrow the same thing twice");
        }
        Self { data, borrowed }
    }
}

impl<T: ?Sized> Drop for DynBorrower<'_, T> {
    fn drop(&mut self) {
        *self.borrowed = false;
    }
}

impl<T: ?Sized> Deref for DynBorrower<'_, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        self.data
    }
}

impl<T: ?Sized> DerefMut for DynBorrower<'_, T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.data
    }
}