[KenanSulayman]

Interestingly this is very similar to how I implemented passing closures into JavaScriptCore as hooks for JS class invocations ("function calls"). [0]

Essentially it's taking advantage of the fact that closures are static methods with "implicit" data pointers. It should be fairly obvious that this is a massive violation of safety and undefined behavior, and most likely to break when debugging symbols etc. are inserted.

The safest way to do this until Rust has figured out a stable-enough-ABI for closure passing would be a thread-local trampoline, I guess. Not very nice..

[0] https://github.com/psychonautwiki/rust-ul/blob/master/src/he...

[Gibbon1]

I read an article by a guy talking about stupid C tricks. One of them was to 'mangle' raw pointers into an index before passing them. And then de-magle them to get back a raw pointer. Advantages are you can pass meta data with the 'pointer'. Which also allows you to invalidate a pointer. The pointer can't be dereferenced. The enclosed variables/data isn't accessible and cannot be modified by the target.

For callbacks the overhead likely isn't significant.

[doomrobo]

Where's the UB? It casts a boxed closure to a raw pointer, and then back to a boxed closure. There's no tricky introspection being done here.

[KenanSulayman]

I'm not entirely sure you read the code I'm referring to. There's no box there.