Function inv_mut 

pub fn inv_mut<'out, T>(out: &'out mut [T; 2]) -> &'out mut [T; 2]
where
    for<'a> T: One + Neg<Output = T> + MulAssign<&'a T>,

Example

let mut v = [1; 2];
vec2::inv_mut(&mut v);
assert_eq!(v, [-1; 2]);