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  • Hacker News
  • Constant headache in C++ with `std::vector` element references. Zig's explicit stability here is a welcome relief for data structures.
    by Prydown
  • It seems you misunderstood. It's not an explicit stability guarantee (such things is not possible), it's a debugging helper to crash the program more easily when it happens, requiring you to annotate the code.
    by afdbcreid
  • C++ developers constantly wrestle with `vector` iterator invalidations. Good on Zig for making this a first-class concern.
    by stub_out
  • How does Rust avoid this?
    by brcmthrowaway
  • It took me a minute to understand that this asserts on pointer change within the container, rather than lock/unlock the data structure like a SDL surface.

    I recently implemented a custom C++ container for a path whose components could be iterated, backed by a std::string. I just store indices and a reference to the string, such that my iterators are not invalidated if the std::string gets reallocated after being modified. Far less error prone for little added cost.

    by boricj
  • Aside: one Zig (syntax) feature that I really missed in Rust is shown in the second code block, namely prefixed multi-line string literals à la:

        const text =
        \\This is a long comment
        \\But I can split it among lines arbitrarily
        \\And keep my indentation.
    ;
    I've started using the Rust macro library `docstr` [1], which does the same thing:

        const TEXT: &'static str = docstr!(
        /// Now I can do it in Rust, too.
        /// I prefer this style a lot of the time
        /// for long texts.
    );
    It even works with macros (example from the docs):

        let greeting: String = docstr!(format!
        /// Hello, my name is {name}.
        /// I am {} years old!
        age
    );
    1. https://docs.rs/docstr/latest/docstr/
    by Rendello
  • In C you can do that.

       printf ("Things:\n"
     " thing1=%u\n"
     " thing2=%u\n"
     " thing3=%u\n",
        thing1,
        thing2,
        thing3);
    by Gibbon1
  • C# solves this so elegantly

       string text = """
      This is a long comment
      But I can split it
      And keep my indentation.
      """;
    by metaltyphoon
  • This makes a lot of sense if you consider that it is consistent with the rest of the language. It is one more way to set up tripwires in your code to to catch your own programming errors. Similar to using asserts in your functions to vet input and output.

    I use Array list a lot so excited to add this throughout the code to harden them.

    I can imagine this is not everyone's cup of tea, but then you probably also wouldn't enjoy any of the other explicitness.

    by portly
  • This is a gripe of mine, and I will admit it is weak.

    Changing a segfault to a panic with a stack trace is an improvement in developer experience. It does not make better software. The advantage of automatic strategies to mitigate memory safety mistakes either by using GC to make the program sound or static analysis to prevent the mistake by construction is plainly better.

    There is a direction in some systems programming circles away from this by eschewing "complexity" (in other words, fixing the damn problems) for programs that have better error messages when the programmer made a mistake. I don't see that as better software.

    by duped
  • They forgot to add (I believe this was not deliberate, maybe their users already infer that) that this only actually performs the check on Debug and ReleaseSafe modes, not on ReleaseFast mode. Which is reasonable I guess because this is a memory write/read/branch in a super hot code path, but undermines a large part of the guarantee in my opinion (doesn't Zig have a debug allocator that could catch the mistake in the example just as well?).
    by afdbcreid
  • Debug allocator can't catch it because it's not an allocation bug. Debug allocator finds bugs by marking memory during alloc/free and inspects them upon deinit. Pointer to a memory location change is not something allocator has control over. Possible solutions: smart array list implementation (this article), move semantic analysis (Rust's borrow checker), runtime introspection (https://fil-c.org/).
    by ivanjermakov
  • It's a nice feature but I can't help feeling like, if you need a stable pointer to an item in a collection, ArrayList is the wrong data structure to use? Maybe someone can chime in and give me an example of when you'd do this instead of, e.g., just storing an index. Alternatively, you could use an Unrolled Linked List (FKA SegmentedList in Zig before it was removed in 0.16, not sure why).
    by _bohm
  • My mental model of Zig is that it is explicitly the language for developers who prefer using pointers in business logic (instead of just in MMIMO, and are looking for something with improvements over C); i.e. exactly this class of abstraction.
    by the__alchemist
  • Maybe one use case is if you are interfacing with external C library and you're stuck with pointers?
    by beepbooptheory
  • ArrayList is a very generic (pun not intended) structure and could be stretched quite freely in any direction with useful property of owning underlying slice. Like readonly preallocated ArrayList is a thing.
    by bvrmn
  • I use it in a lot of places where I know the max capacity ahead of time -- ensureCapacity() followed by a lot of *AssumeCapacity()-styled commands. It's convenient for all of the ... convenience ... methods (append() requires some bookkeeping somewhere, appendSlice() requires more, and so on). In those usages, it's basically syntactic sugar over a slice. That's not a perfect solution, but it's reasonably good often enough that I keep doing it.

    The proposed change doesn't do much for me personally (memory safety is ensured in other ways, and if it weren't I wouldn't be annoyed debugging the allocator-observed errors), but I could see myself using it at some other point in time for the same class of usages, or I could see other people relying on it when they choose that class of coding.

    by hansvm
  • SegmentedList had a weird API, especially the way you control the list growth factor by the size of an inline array. And it hadn't kept up with stdlib norms in recent versions. I do hope it comes back eventually with an improved API.

    At least we got Deque in exchange. I use that far more often than I used SegmentedList.

    by nvme0n1p1
  • I don't know Zig, but conceptually: a direct pointer is the fastest way to access an object. An arraylist is the fastest dynamic sequence of objects (fattest in access, not in growth). You use these when you need the performance. It's not often but it certainly happens. The most trivial example is a string that you append to but still need to pass to a C API in between that expects it to be contagious, but it's far more useful than just for storing characters.
    by dataflow
  • I count this as a "rookie at system programming" mistake alongside returning a reference to a local variable. Rust is great at this because borrow checker can catch those at compile time and it can _teach_ devs to not do that.
    by ivanjermakov
  • This seems weak.

    In a language like Rust, the compiler will “lock” the pointers for you, and you can’t forget.

    In a language like C++ (and presumably Zig), one could, in theory at least, have the iterators and slices that reference the storage of a dynamic array hold some sort of lock that pins the storage.

    But this API requires the programmer to remember to lock the pointers and also requires the programmer to keep the lock alive for the correct region of code. And it looks to me like even the example in the blog post has the lock taken completely outside the function that requires stability, so there is nothing whatsoever that gets the lock scoping right. Even the type system can’t help — the offending parse function can’t declare that it wants a pointer-locked ArrayList parameter.

    by amluto
  • 2026 and developers still use memory unsafe languages. I hope we get regulated at this point, disgusting.
    by insanitybit
  • I reach for a low-level language only when I want low-level control over what operations happen and when, what memory is used and when etc.. At present, no language offers me this control and safety at the same time. With Rust, when I need such control (which is always, otherwise I would use a higher-level language), I need to give up safety, anyway, at which point I have no safety and the complexity of a language that offers safety.

    So right now, when we want control, we need to give up some safety, but weaker things are still helpful.

    Also, in low-level code, the problem of "I might forget to do something" sometimes clashes with the problem of "I need to see exactly what operations are done and where". Various kinds of implicitness help with the former at the expense of the latter.

    I'm not saying this is universally better than other approaches, but many people who do serious low-level programming would prefer this.

    by pron
  • Do any languages have a notion of "relative pointers"? So in the example if instead of appending "line" as ptr & len, it'd instead be appending an offset & len which could in theory be used to safely compute the actual location even with relocations.
    by frmdstryr
  • This is how it is with languages which provide less guarantees than Rust. Sure you can try to hold all the invariants and restrictions in your head, but a sufficiently advanced compiler can do this for you without the possibility of making mistakes. I have no idea why people claim that's too restrictive - if you're not enforcing those rules manually you're just setting yourself up for issues down the road.
    by slopinthebag
  • I agree. https://news.ycombinator.com/item?id=49501582 says:

    “I use it in a lot of places where I know the max capacity ahead of time -- ensureCapacity() followed by a lot of AssumeCapacity()-styled commands. It's convenient for all of the ... convenience ... methods (append() requires some bookkeeping somewhere, appendSlice() requires more, and so on). In those usages, it's basically syntactic sugar over a slice”*

    I suspect “where I know the max capacity ahead of time” covers most if not all use cases (if it you use this without knowing max capacity, you either accept your code may panic, or you do some unlock, grow, lock again dance when you discover your initial estimate is wrong)

    If so, wouldn’t adding a growable container where you specify capacity at construction time and removing access to the internal pointers of ArrayList be a better way to handle this?

    by Someone
  • To make matters worse, there’s also a weaker documentation problem. Where should one learn that they need to do this? zig.guide’s page on ArrayList doesn’t mention it. https://ziglang.org/documentation/master/std/#std.ArrayList doesn’t mention it, https://ziglang.org/documentation/master/std/#std.ArrayList doesn’t mention it at the top level, just a method in the midst of dozens of other methods. I honestly don’t know how one is meant to discover this outside of random blog posts.
    by mirashii