test.rs

    ///Modifies data via temporary serialization
    pub fn modify<F: FnOnce(&mut Data)>(&'de mut self, cb: F) -> io::Result<()> {
        let new_data: Vec<u8> = {
            let data = self.inner.as_slice();
            let mut data = Ser::deserialize(data)?;
            cb(&mut data);
            Ser::serialize(&data)?
        };

        if new_data.len() == 0 {
            Err(empty_write_error())
        } else {
            self.inner.put_data(&new_data)?;
            self.inner.flush_sync()
        }
    }

error[E0502]: cannot borrow `self.inner` as mutable because it is also borrowed as immutable
   --> src\serializer\mod.rs:149:13
    |
138 |             let data = self.inner.as_slice();
    |                        ---------- immutable borrow occurs here
...
149 |             self.inner.put_data(&new_data)?;
    |             ^^^^^^^^^^ mutable borrow occurs here
...
152 |     }
    |     - immutable borrow ends here