> All GC implementations in Rust that I've seen so far relied on much more heavy handed techniques like having GC<T> to be a double indirection, pushing referen

> All GC implementations in Rust that I've seen so far relied on much more heavy handed techniques like having GC<T> to be a double indirection, pushing references to threadlocal queue, have GC pointers to be fat to pass around metadata inline, etc. They have been closer to modified RC with corresponding cost. For reference, the gc-arena crate discussed in the blog post has no double indirection and no fat pointers (except for DSTs). Passing and reading the references is free, while assigning references to GC objects requires a write barrier, like in C#. The library is single-threaded, so there's no thread local state (and no global state). But you're right that since the library is not _that_ invasive or integrated with the language runtime / allocators, you don't get things like cheap allocations, barrier omitting or generations. And most notably, without stack scanning you can't do collection while in a GC-aware scope - in particular, you can't automatically run GC if you run out of memory during an allocation. Piccolo (Lua VM) solves this by being stackless and repeatedly jumping out of the GC scope, while Ruffle (Flash/AS2/AS3 VM) bites the bullet and only runs collection between frames and hopes that it'll never hit OOM within a single frame.