Simulate __exit__ using Drop trait

[AsafFisher]

If one want to use a with statment with a pyclass then __exit__ can be automatically implemented by calling drop on the pyclass.
This elimnates the need to implement a __exit__ function.

#[pyclass]
struct DebugController {
    conn: TcpStream,
}
impl Drop for DebugController{
    fn drop(&mut self){
        // Do RAII stuff idk send bye bye message using the socket
    }
}

with DebugController as d:
        d.do_stuff()

I am thinking about it and not sure if it's a good idea... because implementing __exit__ might seem easier.

[birkenfeld]

Hey Asaf, can you elaborate a bit? I'm not sure what you're proposing here.

[AsafFisher]

Ultimately if a struct impl Drop then __exit__ can be automatically implemented to call the drop function

[birkenfeld]

AFAICS that wouldn't be possible, since there's no guarantee in Python that the context manager object is destroyed at that point.

And if the Python object is still alive, the underlying Rust object must stay alive as well, so it can't be dropped.

[davidhewitt]

Agree with @birkenfeld

To give some additional detail here, in general we don't automatically implement any Python methods based on the existence of a Rust trait. I think to do that would probably require specialization.

Also, some other discussion about Drop and __exit__ can be found at #1205 (comment)