Programmers can often improve the performance of their programs by reducing heap allocations: either by allocating on the stack or reusing existing memory in-place. However, without safety guarantees, these optimizations can easily lead to use-after-free errors and even type unsoundness. In this paper, we present a design based on modes which allows programmers to safely reduce allocations by using stack allocation and in-place updates of immutable structures. We focus on three mode axes: affinity, uniqueness and locality. Modes are fully backwards compatible with existing OCaml code and can be completely inferred. Our work makes manual memory management in OCaml safe and convenient and charts a path towards bringing the benefits of Rust to OCaml.

@article{LorenzenWDEL24,
  title = {Oxidizing OCaml with Modal Memory Management},
  author = {Anton Lorenzen and Leo White and Stephen Dolan and Richard A. Eisenberg and Sam Lindley},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {8},
  number = {ICFP},
  year = {2024},
  doi = {10.1145/3674642}
}