pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
        if index < self.len() {
            let idx = self.wrap_add(self.tail, index);
            unsafe { Some(&mut *self.ptr().add(idx)) }
        } else {
            None
        }
    }
Reserves capacity for at least `additional` more elements to be inserted in the given
`VecDeque`. The collection may reserve more space to avoid frequent reallocations.

# Panics

Panics if the new capacity overflows `usize`.

# Examples
benchmarks/haystacks/code/rust-library.rs