Mostly I think you're right, though I don't think this is pointer tagging a la PAC or auto-zeroing (etc.) a la MiraclePtr, this just looks like compiler support for unique_ptr.
I'm with you on the high RAII: it sounds like destructors with some important missing steps. It also looks like the idea of "SOPs must eventually be freed" runs into some immediate Turing problems, i.e. you can't know an SOP will be freed when you have if statements, or a cycle of functions passing an SOP around that conditionally free an SOP depending on some external state, or program behavior contingent on external messaging, etc.
I think another place you'd run into problems with this is... you actually do want references to heap allocated memory. It's pretty laborious to get by with unique_ptr all on its own; you want to lend out shared references that you get back as their scopes close, and so on. It doesn't seem like there's any facility for that here.
To people trying to build systems like this without building Rust's system: honestly just try it in C++. Sure there won't be compiler support for it, so you'll have to manually insert stuff, but just see how workable it is. If you were working with this system in a program of any appreciable complexity you'd immediately realize:
- You don't reliably know when things haven't been freed
- You really want references
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An interesting alternative way to look at what's proposed here is, this just an oblique message passing system.
I'm with you on the high RAII: it sounds like destructors with some important missing steps. It also looks like the idea of "SOPs must eventually be freed" runs into some immediate Turing problems, i.e. you can't know an SOP will be freed when you have if statements, or a cycle of functions passing an SOP around that conditionally free an SOP depending on some external state, or program behavior contingent on external messaging, etc.
I think another place you'd run into problems with this is... you actually do want references to heap allocated memory. It's pretty laborious to get by with unique_ptr all on its own; you want to lend out shared references that you get back as their scopes close, and so on. It doesn't seem like there's any facility for that here.
To people trying to build systems like this without building Rust's system: honestly just try it in C++. Sure there won't be compiler support for it, so you'll have to manually insert stuff, but just see how workable it is. If you were working with this system in a program of any appreciable complexity you'd immediately realize:
- You don't reliably know when things haven't been freed
- You really want references
---
An interesting alternative way to look at what's proposed here is, this just an oblique message passing system.