I agree that RAII does not solve everything - in particular, issues with memory fragmentation. However, I prefer the direction being taken by Rust and suggested by the top level poster: rather than having to run a separate thread which tries to infer which resources are no longer needed, with potentially large runtime costs, instead augment the language semantics with a clear ownership model, and thereby give the compiler enough information to generate code that runs in a stable, predictable memory footprint.

That reminds me of the VILW argument: we will make languages really expressive and compilers really smart, then we can get rid of fancy CPU hardware that do instruction scheduling dynamically.

It doesn’t always work. A dynamic tracing GC (or reference counting or using arenas) can be more efficient in ways that static approaches probably won’t be able to effectively emulate. Rust is a great experiment for seeing how far we can go in this area, so we will see.

RAII has nothing to do with memory fragmentation.

Solving memory fragmentation requires moving objects around. Usually you get that via a moving (or compacting) garbage collector. But there's no reason RAII style resource allocation couldn't move things around.

And there are plenty of garbage collection strategies that don't move objects around.

I was simply stating that RAII does not solve the memory fragmentation issues. Many GC's do solve the memory fragmentation issue.