volatile_cell has undefined behaviour

[huonw]

• it is not legal to mutate data through a & pointer unless that data is contained in an UnsafeCell

• the T type has no bounds, and so can be used to duplicate arbitrary data, e.g. this prints the same pointer twice:

  fn main() {
    let x = VolatileCell::new(Box::new(1));
    let y: Box<i32> = x.get();
    let z: Box<i32> = x.get();
    println!("{:p} {:p}", y, z);
  }

  If this is trying to behave like std::cell::Cell, this could be fixed by bounding T: Copy.

[farcaller]

Fixed, thanks for pointing it out.