Re: [Libguestfs] [PATCH] Rust bindings: Implement Event features

On Tue, Jul 30, 2019 at 09:43:26PM +0900, Hiroyuki Katsura wrote: But both of the things are trying to accomplish the same thing, my question was why are you using _both_ approaches to keep the pointer valid? Oh, it *has* to have one, the only one that you can choose here is 'static. For callbacks that can get called multiple times, yes. Or until you delete it at which point you can clean it. So I'm misunderstanding the documentation probably. From Box::leak: "This function is mainly useful for data that lives for the remainder of the program's life. Dropping the returned reference will cause a memory leak. If this is not acceptable, the reference should first be wrapped with the Box::from_raw function producing a Box. This Box can then be dropped which will properly destroy T and release the allocated memory." Just for completion sake, Box::into_raw: "After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory. The proper way to do so is to convert the raw pointer back into a Box with the Box::from_raw function." Which, I feel, is a different wording of the same situation. Especially since both of them can then be used with Box::from_raw(). The only difference being that one returns pointer and the other one a reference (which can have a lifetime associated with it). Actually, thanks to the awesome way the docs work, I can just click the `[src]` link and find out that: pub fn leak<'a>(b: Box<T>) -> &'a mut T where T: 'a // Technically not needed, but kept to be explicit. { unsafe { &mut *Box::into_raw(b) } } Anyway, I must admit that even though I am talking about this like it was written badly, I actually do not know about a better way if the handle can be dropped while the callback is executing. So maybe the question is, can this really happen?