166         // INVARIANT: The refcount is initialised to a non-zero value.  in try_new()
211         // INVARIANT: By the safety requirements, the invariants hold.  in from_inner()
265         // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is  in deref()
279         // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero.  in clone()
280         // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is  in clone()
291         // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot  in drop()
297         // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and  in drop()
298         // this instance is being dropped, so the broken invariant is not observable.  in drop()
299         // SAFETY: Also by the type invariant, we are allowed to decrement the refcount.  in drop()
410         // INVARIANT: The safety requirements guarantee the invariants.  in new()
433         // SAFETY: By the type invariant, the underlying object is still alive with no mutable  in deref()
521             // INVARIANT: The newly-created object has a ref-count of 1.  in try_new()
528         // INVARIANT: The refcount is initialised to a non-zero value.  in try_new_uninit()
535             // INVARIANT: The newly-created object has a ref-count of 1.  in try_new_uninit()
608         // SAFETY: By the `Arc` type invariant, there is necessarily a reference to the object, so  in deref_mut()