Comment by masklinn | Hacker News Reader

Comment by masklinn | Hacker News Reader

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> You can’t really do that in rust because you’d have to give ownership of the file/folder/whatever to the closure - meaning you can’t use it yourself afterwards!

The way to do this is pretty much what C++ has in unique_ptr(p, deleter): have the utility RAII class own both the object and the closure, dereference to the wrapped object, and on drop pass the wrapped object to the closure.

Altho

> Eg if I’m creating a temporary file or directory in a function to handle some IO logic, I’ll create a RAII wrapper around a closure that deletes that folder when the scope expires

There are crates for lots of those situations.

https://crates.io/crates/tempfile for instance.

> have the utility RAII class own both the object and the closure

Yeah, but the ergonomics suck. Especially for random cleanup tasks that aren’t necessarily one-object, one-task.

The temp file thing was just an example, actual use case was more domain-specific.

> Yeah, but the ergonomics suck. Especially for random cleanup tasks that aren’t necessarily one-object, one-task.

Doesn’t seem much more of a problem? Put a tuple in, get references out, cleanup gets the entire tuple.

If lifetimes get complicated, use refcells and / or Rcs.

If it's only a temp file (as opposed to a dir) and it's Linux, you may want to use O_TMPFILE (possibly O_EXCL too) when open()ing the file instead of the RAII wrapper. That ensures the OS will delete the file even if the program is killed.

https://docs.rs/tempfile/3.3.0/src/tempfile/file/imp/unix.rs...

An additional (and more important) constraint to being on Linux and creating a single file is that this assumes you are the one creating the file, which is oftentimes not the case. e.g. in my rust ffmpeg wrapper, I have pipelines that invoke ffmpeg and through it create multiple intermediate files that need to be cleaned up at the end of the run in all cases (success and failure).

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