OCaml is surprisingly good about letting you switch in and out of this style, on a module by module basis.
It’s not quite a zero-alloc application, but Incremental is a good example of a library that has been heavily optimized to avoid allocation, and does a few tricks using the OCaml’s unsafe APIs to make it possible.
Rust, for what it’s worth, also requires you to use unsafe APIs to do the full range of things that are required in a high-performance system that makes good use of the hardware.
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