It works for Sphinx because the scope of the GC is restricted to Sphinx code. The Sphinx language runtime itself is typical Rust code - no GC used. So it is fai

It works for Sphinx because the scope of the GC is restricted to Sphinx code. The Sphinx language runtime itself is typical Rust code - no GC used. So it is fairly straightforward to ensure that GCPtrs are never dereferenced during a collection cycle. Essentially, collection only ever happens between instructions. If we were writing a GC for general Rust code then this and other issues around ensuring values are rooted would become much bigger problems. For example, the rust-gc crate has to deal with these. Just to be safe I took a page out of rust-gc's book and implemented a guard to ensure that the runtime will at least panic if I make a mistake and that happens.