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עַם יִשְׂרָאֵל חַי Slava Ukraini 🇺🇦 ❤️ 🇮🇱

  • 28 Posts
  • 139 Comments
Joined 1 year ago
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Cake day: June 14th, 2023

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  • The reason I said to use rvalue references is because otherwise it is an apples-to-oranges comparison: in the C++ code you have implicit ABI decisions around the call convention and whose responsibility it is to destroy the temporary.

    Yes, sure, compiling in one translation unit helps, but as I mentioned above, passing an owning pointer between translation units shouldn’t be inherently inefficient

    https://godbolt.org/z/9875qMM6Y (or alternatively: https://godbolt.org/z/9xehs3sYP)

    The assembly is identical, the ownership is clearly transferred, and this doesn’t need LTO or looking at the function bodies and is entirely done by the C++ compiler. It involves using (when available) a vendor attribute (see trivial_abi, shouldn’t be an issue given Rust devs are fine with having only one compiler anyway) and writing a UniquePtr class (shouldn’t be used in production code, what I’ve given there is only for illustration purposes) that assumes that the custom deleter cannot have an internal state.

    This is a zero-runtime-cost abstraction. Now whether the zeroing of that cost can depend on what ABI assumptions you’re ready to make, or whether you want to depend on LTO is another thing. We’re literally discussing a “problem” that is not really a problem because Rust doesn’t have the luxury yet to have that problem: you’re easily forgetting that Rust has only one compiler.

    Carbon was announced in 2022

    A project like that usually takes years, so again, very likely that they began working on it years before that. For instance, Google designed Go in 2007 and announced it in November 2009.






  • That’s a bad apples-to-oranges comparison, unique_ptr frees memory upon destruction, which with the raw pointer version you don’t do. The least you could do is use rvalue references. The class layout of unique_ptr is also hard to optimize away (unless via LTO) because consume isn’t in the same translation unit and the compiler has to let your binary be ABI compatible with the rest of your binaries. (Also, you’re using Clang 9 by the way, we are at version 17 now)

    This is much fairer: https://godbolt.org/z/v4PYcd8hf

    Then, if you additionally make the functions’ bodies accessible to the compiler and add a free to the raw pointer version (for fairness if you insist to have consume or foo destroy the resource), you should get an almost identical assembly code (with still an extra indirection that you’ll see in an extra mov due to the fact that the C++ compiler still doesn’t see how you use them, but IMO that should still be a textbook case for LTO), and the non-zero difference should disappear altogether once you actually use those functions and if it doesn’t you absolutely should file a bug report.

    Carruth, while an excellent presenter, has been on a “C++ standard committee bad, why don’t we do more ABI-breaking changes, y’all suck, Abseil and Carbon rule” rant spree, with that basically materialized by Google stopping active participation in Clang (haven’t followed the drama since then so not sure if Google backtracked on that decision), and it’s hard to consider him to be objective about this since he also has the Carbon project and his recent Carbon talks are painful to watch as it’s hard to ignore how he’s going from a “C++ optimization chad” that he used to be to a Google marketing/sales person.


  • Rust developers are already known (/memed) to be elitist about Rust

    They’re also extremely toxic. An example from 4 months ago when they vandalized cppreference.com :

    The meme is that most Rust devs merely shout slogans like “memory-safety” without knowing what they mean, precisely because many of them come from web dev backgrounds (this video by Prime Time proves why that’s problematic: https://www.youtube.com/watch?v=Wz0H8HFkI9U , the guy has no clue what std::unique_ptr is) and have never touched a pointer in their lives. Easy and “appealing to hobbyists” languages are always an issue as the community usually ends up becoming toxic and full of wrong practices being normalized, and a prime example of that is PHP.

    Another example is how Lemmy initially struggled to handle 10k~20k users during the Reddit exodus despite the backend being written in the “ultra-fast memory-safe totally-will-replace-C++” Rust. Why? See this: https://github.com/LemmyNet/lemmy/issues/2877 and they were doing stuff like joining huge-ass tables before the filtering. If phiresky didn’t save them with his SQL prowess Lemmy would have literally died and its backend being written in Rust would not have changed a single thing.

    Rust gives hobbyists the illusion that their projects will suddenly become fast and bug-free if they write them in Rust, and they don’t even hide that mentality as you can see that on almost every single project that’s written in Rust they list “written in Rust” as the main selling argument. This is probably the only language I’ve seen where this happens.

    Now as for the “Java bad”, I’m kind of guilty of it too. I very much dislike how academia is obsessed with UML diagrams and the “Java way” of seeing OOP and interfaces everywhere. CPUs and GPUs do not think in OOP. They do not see “objects”. They see data, registers, caches, branches but certainly not your “beautiful abstract class”. When you think you did a good job of crafting a “clean” UML diagram with lots of “nice interfaces” which you then implement using virtual polymorphism in C++ and abuse dynamic_cast, you’re torturing the CPU with indirections, cache misses and branch mispredictions. Dynamic polymorphism and virtual inheritance in particular should not be the standard way to solve problems, yet that’s exactly what academia teaches and most of those who push those ideas coincidentally also happen to be from Java backgrounds and that’s why the “Java bad” meme is still alive.

    That said, beyond academia, I think it’s obviously stupid to religiously shit on Java. Lot’s of advanced features are coming out, Android is a thing thanks to Java and lots of web services are working with high reliability thanks to it. Also obviously, one has a much better chance at landing a high-paid software engineering job if one knows Java than if one knew only Rust.