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Comment by azangru | Hacker News Reader

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azangru·

Surprised it's not OCaml; they've invested highly in OCaml.

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In their frontend, yes. The Flow JS typechecker, and (kind of) Reason.

Backend and infrastructure sees more Rust though. Eg the Mercurial server implementation.

How’s the OCaml multi core rollout going these days? IIRC shared memory parallelism requires FFI still.

The primary reason they stated is memory safety as this is gonna be really critical stuff dealing with money. Also no GC.

OCaml is more memory safe than Rust (as the "unsafe" parts are harder to access). But it does have GC, so GC is likely the primary reason.

I wouldn't label Rust as being less safe than OCaml. You have to explicitly opt-in to any unsafe operations. More often than not, the unsafe blocks are needed because the compiler can not check all of the invariant cases.

Does OCaml even have a way of shedding memory safety?

OCaml is an "obligate-GC" language.

Most languages that offer optional GC, including Rust (with its RC and ARC boxing) and C++ (with std::shared_ptr), implement it mainly via reference-counting.

Yes, the `Unsafe` module (well, at least used to have it... fairly undocumented... maybe it's been removed?).

Oops, I misremembered the name. @pcwalton is right, it's called `Obj`.

Sure. Obj.magic is a bit cast.

> You have to explicitly opt-in to any unsafe operations

Many of the unsafe operations don't exist in OCaml. Often because the GC makes them unnecessary.

You can implement all of the unsafe operations in OCaml using the unsafe Obj.magic cast: http://caml.inria.fr/pub/docs/manual-ocaml/libref/Obj.html

I mean, you can just use #[forbid(unsafe_code)] if you really want to. You do have to audit your dependencies, but that's true with OCaml as well (call Obj.magic and all bets are off).

Less so these days: https://github.com/facebook/hhvm/tree/master/hphp/hack/src/p...

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