There's already a precedent of ownership on transferred objects. Why not have an `.unsafe(cb)` method on the structs? Error if you don't have ownership, then us

There's already a precedent of ownership on transferred objects. Why not have an `.unsafe(cb)` method on the structs? Error if you don't have ownership, then use the callback to temporarily acquire ownership. At least to me, it's more intuitive and seems idiomatic.