[DanWaterworth]

If you are consuming an API that provides an object with a destructor, you are correct, you can determine when destructors will be called.

The issue is when you produce an API that contains objects with destructors. Since you are handing these entities off to unknown code, you cannot ensure that they will be dropped. This was a problem in scoped threads in Rust.

[siscia]

Can you please dig deeper, that I am not sure I follow.

In which case in rust you cannot be sure that "the drop" will be called?

[dbaupp]

If there's a cycle of strong references with Rc or Arc (or shared_ptr in C++), those objects still never get dropped/have their destructors called.

[richardwhiuk]

A Rc cycle causing a leak.

See the very excellent http://cglab.ca/~abeinges/blah/everyone-poops/