Hard (normally memory-unsafe) cast:
Cast contents to another type, and returns an instance with that contents.
The current instance is cleared. U may have an incompatible constness.
To enforce memory safety, the current instance must be the only one
holding a reference to the data (call ensureUnique first).
No copying is done.
Hard (normally memory-unsafe) cast: Cast contents to another type, and returns an instance with that contents. The current instance is cleared. U may have an incompatible constness. To enforce memory safety, the current instance must be the only one holding a reference to the data (call ensureUnique first). No copying is done.