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> I've never understood that to mean that every possible abstraction would be zero cost, but that the language itself provides abstractions that are zero cost.

• saghm 10mo ago
  > But the point is that the exact same external library code has a _lower_ cost if called from the non-abstract horror of a language C, and the (partial) fix for that is really ugly looking low-level Rust crap that that took a _long_ time to figure out and is the exact opposite of an abstraction, and the full fix is not even known yet. No, it's not the exact same external library. There's an additional Rust library in between that they used, which provides the `FFISafe` type, and that has overhead. This is not a standard Rust library, or even one that I'm able to find within a few minutes of googling despite having used Rust for over a decade. It's not clear to me why you think this is necessarily representative of Rust rather than one specific library; someone could just as easily wrap a C library in another C library in a way that adds overhead, and it would be equally nonsensical to cite that as an argument that C isn't efficient. Your argument seems to boil down to "Rust claims to be efficient, but it's possible for someone to write inefficient code, and for me to use that code, so therefore those claims are wrong".
  • zephen 10mo ago
    > No, it's not the exact same external library. It uses the exact same assembly language. > There's an additional Rust library in between that they used, which provides the `FFISafe` type, and that has overhead. Look, I wrote " But the point is that the exact same external library code has a _lower_ cost if called [from C]" and that remains a true statement. It's pretty obvious that I was referring to the shared code, otherwise, it wouldn't have ever been called from C, right? The profiler showed that the identical assembly language itself was taking more cycles when called from C. > There's an additional Rust library in between that they used, which provides the `FFISafe` type, and that has overhead. This is not a standard Rust library, or even one that I'm able to find within a few minutes of googling despite having used Rust for over a decade. The point is that they did the absolute normal expected thing in Rust, and it slowed down the external assembly language library, and after a _lot_ of digging and debugging, they changed the Rust code to be a lot less flexible and more convoluted, and now the assembly language is almost as fast as when it is called from C. > Your argument seems to boil down to "Rust claims to be efficient, but it's possible for someone to write inefficient code, and for me to use that code, so therefore those claims are wrong". No, that's not my argument at all. Look, the people doing this _obviously_ know Rust, and it took them a _long_ time, and some _really_ ugly concrete low-level concrete code, to take external code and make it perform almost as well as if it had been called from C++. To me, that looks like a high-cost non-abstraction.
    • Aurornis 10mo ago
      > Look, I wrote " But the point is that the exact same external library code has a _lower_ cost if called [from C]" and that remains a true statement. I don't think you've understood the article at all. The overhead came from the author's own abstractions that were designed to accommodate both the assembly version or the Rust fallback. The assumption was that they take the same types and therefore the abstraction would be zero-cost, but in practice the Rust version had different types and therefore there was extra overhead in the way they were called. If the author had simply done an extern "C" of the function and called it from Rust there wouldn't be overhead. > To me, that looks like a high-cost non-abstraction. The abstractions that caused this probably were not standard Rust library abstractions. The author wrote them as part of the library. You don't need an abstraction at all to just call C functions from Rust. It's build right into the language. If you think the problems in this article are a common Rust failure mode, you haven't understood the article at all. The unique method of calling C functions was something the author wrote, not a standard Rust practice.
• Aurornis 10mo ago
  > if called from the non-abstract horror of a language C, and the (partial) fix for that is really ugly looking low-level Rust crap that that took a _long_ time to figure out and is the exact opposite of an abstraction, In case it's not clear, the FFISafe abstraction is not a Rust standard library feature. It's a wrapper type that the author created within their library to bypass some compiler warnings: https://github.com/memorysafety/rav1d/blob/25e5574/src/ffi_safe.rs#L11 https://github.com/memorysafety/rav1d/blob/25e5574/src/ffi_s... If you want to call C functions from Rust it's as simple as writing an extern block and then calling the function, though you'll have to put the call in an unsafe block because obviously the Rust compiler can't make safety guarantees across that boundary. The Rust docs for extern are concise: https://doc.rust-lang.org/std/keyword.extern.html https://doc.rust-lang.org/std/keyword.extern.html