13 notes
Single ownership with deterministic destruction, multiple simultaneous borrows allowed, runtime borrow-count enforcement. No GC, no compile-time borrow checker, no lifetime variables. Concurrency uses `uni T` (unique values) for safe inter-process transfer.
Capability tracking in the type system. Each value's type may carry a capture set listing which capabilities it could reference. Foundation for capability-based effects, separation checking (System Capybara), and ownership for resources.
Linearity attached to function arrows, not to types. Backwards-compatible: ordinary code continues to type-check unchanged. Experimental since GHC 9.0; still labelled experimental in 9.12 / 9.15 (2024–2026).
Orthogonal modes layered onto OCaml's type system. Mode is a property of a value, separate from its type, tracked through inference. Production in Jane Street; open-sourced as OxCaml in 2025.
Swift 6.x has shipped a complete move-only/noncopyable system layered on top of ARC. Parameter conventions are explicit; the law of exclusivity (Swift's variant from 2017) supplies the static aliasing discipline.
Microsoft Research's experimental concurrent-ownership language. Ownership is over **regions** (groups of objects) instead of individual objects. Cowns (concurrent owners) serialise access; behaviours schedule work over multiple cowns atomically.
Six capabilities (iso, trn, ref, val, box, tag) make actor-based concurrency data-race-free at compile time. Production at WallarooLabs and Microsoft; foundation for Verona's region work.
Strict linear types as the load-bearing primitive for memory and protocol safety, plus capability-based effect control. Spec-and-compiler-small enough to read in a weekend.
A Rust-like ownership system with simpler call-site syntax, taped onto a Python-shaped surface, sitting on MLIR, headed to open source in fall 2026.
Mutable value semantics with subscript-based projection borrowing, no lifetime variables, and the Law of Exclusivity enforced at call sites.
The direct intellectual ancestor of vm3's handle design: a per-allocation generation counter, a per-reference remembered generation, and a check on every dereference. Same idea, different layer.
The state of Rust's borrow checker as the Polonius "alpha" lands behind a nightly feature gate, and what a non-ownership language can still steal from it.
Rust+Polonius, Vale generational references, Hylo, Mojo, Austral, Pony, Project Verona, Swift, OxCaml, Linear Haskell, Scala 3 capture checking, Inko.