[stinos]

> Why should people complexify and uglify their C++ code with the uint8_t pointer (or std::byte), when void* works just fine??

Fair point (although to be honest: 'complexify' feels a bit of an exaggeration here to me), but the answer to this why is simple: document and express intent clearly. The compiler gave you an error first such that you're forced to consider what you're doing. Any seasoned C++ developer seeing this knows what this reinterpret_cast means.

> Wow. With std::span the complexity-meter bumps in the red zone and goes even higher!

Same remark: yes, it's a bit more text to read, but again: to me (and many others I'm guessing) this clearly expresses intent. I also do not find it particularly hard to read. I mean, it's C++, you're likely going to encounter templates at one point or another, except in super specific software perhaps. But no-one also ever argued the C++ learning curve was easy, and trying to make it easier by refusing to use features which were added for good reasons and instead going back to constructs which are the very source of those reasons seems a bit backwards.

> As a nice addition, if you use SAL annotations, the function could be decorated a bit to help code analyzers detecting memory bugs

Some might also say it complexifies and uglifies the code. And in any case makes it non-portable on top of that.

[VulgarExigency]

It seems unlikely that this is the case, as the author appears to be experienced, but the post reads like the author has never had to maintain a "simple" and "beautiful" function that was mangled into incomprehensibility over the years, and where if a more expressive type signature had been written from the start, it would have restricted the damage caused over time.

[zahlman]

> a "simple" and "beautiful" function that was mangled into incomprehensibility over the years, and where if a more expressive type signature had been written from the start, it would have restricted the damage caused over time.

...Can you give a concrete example? I've been programming literally since the 80s and that doesn't ring true at all for me.

[locknitpicker]

> ...Can you give a concrete example? I've been programming literally since the 80s and that doesn't ring true at all for me.

Even this week I stumbled upon legacy code that started off with a clean function, void DoSomething(Foo). Then a few years passed and someone started using Foo to handle two scenarios, let's call them Left and Right. They could have simply introduce two new types, FooLeft and FooRight. But no. Instead they kept Foo after adding a few extra optional fields, and extended DoSomething(Foo) as

    DoSomething(Foo foo, bool isLeft, bool isRight)

This took place during the mid 2010s.

Where have you been during all this time?

[jerf]

Have you been in static types the whole time? It's a really, really common failure state in dynamic programming languages, the Everything Function, that started out as something simple, but then someone added a flag to make it also do this other thing, and then you need a flag to only do that other thing sometimes, and someone needed to operate on multiple things so they made a string parameter also optionally an array, and later someone allowed it to also be an object with this one method, or maybe another method if it's present because some other team implemented that before the first one and can't switch now, and before you know it it's a free-for-all of people adding flags and options and type analysis and if statements and you have a complete mess. Especially if this function is shared by many disparate teams, each of whom isn't "allowed" to break the others, though a single team can fail this way plenty fine.

You can still do this in static languages, but they do push back a bit more because you don't get the flexibility that dynamic languages offer when it comes to accepting a huge variety of different input types.

I've torn a few of these apart over the years. Never fun. Haven't tried with AI but suspect that would only be a quantitative change rather than a qualitative change. The fundamental problem with fixing these is lack of information about the exponential complexity of possible call mechanisms and the AI will have the exact same information problems I will, just faster.

Edit: One of them that I tore apart ended up being two entirely separate functions slammed together into one by historical contingency. I don't just mean that I broke the functionality down into multiple functions, that's a basic tool of how you tear these down and is nothing of note. I mean that one of the "everything functions" I tore down had two distinct calling patterns that were distinct functions that not only shouldn't have been festooned with so many options, but never should have been one function at all because they weren't even conceptually the same thing or even particularly related.

Think of it as two stages of a straight-line process, that were just jammed together because of the fact they got called at similar times, and the original writers weren't clear on the unrelated nature of the tasks and nobody was able to see it through all the obfuscation until I sat down, very deliberately, and I realized this as I was tearing it apart. I don't remember the details, I tend to remember things very conceptually and thus I have a hard time remembering the details of functions with no conceptual purity, but you can get close by thinking of the function as validating incoming parameters, and then applying the parameters to a database. And people were so confused that despite the fact this function, when tickled correctly, could do it all in one shot, sometimes, kinda, with some caveats, there were places where this function was called first to validate (with flags to shut off the application), and then to apply (with flags to shut off the validation). And to be clear, I mean, I did not realize it either even from my contact with the function over the years. It was only when I sat down with it for hours and systematically tore it down that I figured that out.

[zahlman]

> Have you been in static types the whole time?

In fact, Python has been my most-used language for 15+ years and I rarely use annotations.

> the Everything Function

This doesn't happen in my own code; 10 lines is unusually long for me. In others' code, it comes across that the problem is more to do with not properly splitting up the task (a lot of the time, a reluctance to extract loop bodies, in particular). The case logic does have to go somewhere and it isn't always practical to hide it with polymorphism (which has its own problems; I write my own classes quite a bit less than average I would say, and especially avoid inheritance). It's often better when you have one thing that lays out the case logic explicitly while delegating all the actual work.

But aside from Everything Functions, a lot of code bases have more of a problem with the Everything Class that just contains way too much state and still doesn't neatly refactor the work away (and where there are passing attempts to extract a few lines, they often end up in a "method" that doesn't actually touch `self`).

> I mean that one of the "everything functions" I tore down had two distinct calling patterns that were distinct functions that not only shouldn't have been festooned with so many options, but never should have been one function at all because they weren't even conceptually the same thing or even particularly related.

Yeah, sounds like you work in unusually unpleasant circumstances.

But I don't really see how a lack of type expression leads to this kind of thing. The default assumption for the type of a parameter, in untyped Python, should be: "an object that supports the operations currently used with it in the existing code". Going beyond that is like adding additional methods to a class that hasn't actually been written, and needs to be well considered.

A lot of people on HN don't seem to like dynamic typing. I think it's more that it's not for them, and that's fine. There will always be people with different mental models.

[VulgarExigency]

I can't, as my employer owns the code, not me, but there are several examples in one of the Ruby codebases I unfortunately maintain where I can see this degeneration happen via the git history. A small 8 line method with just two parameters slowly grows in complexity over time, until one day one of the original parameters supports two different shapes, and later on it's not that easy to understand which shape it should have in the specific conditional branch you're trying to fix, and the last person to touch that code left the company 4 years ago.

The fault, of course, ultimately lies with the people who wrote and approved this nonsense, but types, or at least type hints, help to avoid this issue.

[antiframe]

Can you point to it? That doesn't sound like "the language forced all this extra baggage on it due to 'safety'" so much as the developers kept adding functions to the function without rethinking if and how they should.

[VulgarExigency]

My point was not about the safety of the code, it was about the expressiveness, which is also what the comment I replied to was about. If the parameter has an explicit type (instead of no type, as is normal in Ruby, or `void*`, which is the C equivalent), it forces the developer to consider the design of the function, instead taking the path of least resistance because they're inexperienced/incompetent/a large language model/burnt-out to the point where even the thought of opening the file makes them feel the not-anxiety of burnout/<insert reason here>.

[dpark]

> instead of no type, as is normal in Ruby, or `void`, which is the C equivalent*

“void *” is not the equivalent of “no type” from Ruby. “void *” says “I operate on raw memory”. It says exactly the same thing as “byte *”.

For sure you should generally not write a function that accepts a “void *” and then internally casts it to some concrete pointer type and operates on that type, but the problem there is the internal behavior, not the choice of byte vs void pointer.

[lostglass]

Forcing developers to consider and more is harmful though. You're arguing to put all of the forethought upfront, when you have the least context and least understanding of what can go wrong, and carrying that complexity forward rather than starting simple and refactoring over time.

[dpark]

You’re really citing a mess in a Ruby code base caused by lack of typing as evidence for why void * is problematic in C/C++?

These are so wildly different cases that the comparison isn’t meaningful. This is like saying you should wear a helmet while playing tennis because sometimes helmets save bicyclists lives.

[locknitpicker]

> You’re really citing a mess in a Ruby code base caused by lack of typing as evidence for why void * is problematic in C/C++?

If you read GP's post you'll understand it exemplifies exactly the issue that the likes of (void *) present in C.

I mean, read the message, particularly this:

> later on it's not that easy to understand which shape it should have in the specific conditional branch you're trying to fix

That is exactly the purpose of void *. By design. It's a pointer to an unspecified type. The unspecified type is exactly why this thing is used.

[dpark]

> later on it's not that easy to understand which shape it should have in the specific conditional branch you're trying to fix

This is not idiomatic C. I have no doubt that someone (likely many someones) have written a function that takes a void * and then internally does some insane half baked dynamic typing. But I’ve never seen it and it’s not common.

You also cannot fix this behavior by changing the pointer type. The type of the pointer is essentially meaningless in this case.

> That is exactly the purpose of void *. By design. It's a pointer to an unspecified type. The unspecified type is exactly why this thing is used.

This is also the purpose of byte * in the examples. Coercing an arbitrary pointer from void to byte doesn’t accomplish anything. It’s lipstick on a pig at best.

[thomasmg]

I don't have a strong opinion what is better in this case, but my view is:

> document and express intent clearly

Arguably, the void* does that as well?

> Any seasoned C++ developer seeing this knows what this reinterpret_cast means.

Same for void*?

> it's a bit more text to read

If you have to call it many times, this adds up.

> Some might also say it complexifies and uglifies the code

I think the point is that it adds security, which the other options don't. And, it doesn't add complexity on the caller, but only at one place: the implementation.

> makes it non-portable on top of that.

This can be solved.

[stinos]

> Arguably, the void* does that as well?

Sort of (I mean: seeing void* and a size probably means 'arbitrary sequence of bytes' or something like that, but well it's void* so it can be like anything whereas with std::span you get more of a hint what's going on just based on the type), but not at the callsite which is what the author is referring to when it's about reinterpret_cast.

> I think the point is that it adds security, which the other options don't

Imo span also does that to some extent, but already when writing the code and not afterwards in e.g. static analysis. E.g. if I get an std:span<const char> I'd have to do counterintuitive things to misuse it. Annotating a void* still leaves it a void* which I then need to cast to char* if I think that's what it is intended.

Don't get me wrong: I've written my fair share of void* but these days I really feel like there's almost always a better thing which can be used instead. Though I do admit that since I've written and consumed a lot of code with such alternatives I'm not hindered by readability/apparent complexity of it anymore but I understand that's not the same for everyone.

[dpark]

> whereas with std::span you get more of a hint what's going on just based on the type

You don’t if it’s a span of bytes (or equivalent).

Encoding the length in a span is a meaningful thing. But the fact that it holds a random memory pointer labeled “byte” instead of “void” doesn’t change anything.

[throwaway27448]

> Arguably, the void* does that as well?

How do you figure? The type is a pointer to quite literally anything, including nothing (ie a pointer that cannot be dereferenced). If you're working with bytes, indicate this with the type.

[addaon]

> The type is a pointer to quite literally anything

No, it can only be a pointer to an object. It can't be a pointer to a function, for example.

[dpark]

All pointers in C/C++ can point to “nothing”. Swapping “void *” for “byte *” is basically an aesthetic choice.

[throwaway27448]

Right. So why not use a typed reference?

[dpark]

1. void * is a type

2. The functions in question here operate on raw memory. void * conveys the same information as byte *. It’s not untyped vs typed. It’s two different types that convey the same information but require slightly different mechanics to obtain.

3. The author explained his reasoning for preferring void * over byte * (or uint8_t *)

4. A reference also isn’t the same thing as a pointer in C++

[repelsteeltje]

+1

And SAL annotations aren't even C++ proper.

[MaulingMonkey]

> Fair point (although to be honest: 'complexify' feels a bit of an exaggeration here to me)

Both uint8_t and std::byte require a header (<cstdint> or <cstddef>) which may expose you to platform x config specific build failures if you do any conditional #including, and the latter is a whole damn enum class with a strange adversion to arithmetic, where `byte |= 1` becomes `byte |= std::byte(1)`, `byte += 1` becomes `byte = std::byte(std::to_integer<std::uint8_t>(byte) + 1);`, and both become something you can accidentally step into in your full debug builds because it's an actual function call (at least on MSVC - still extra instructions on clang/gcc, but I can see the dang call instruction on MSVC!) instead of a compiler built in.

Not to mention, neither is vanilla C++03... I threw a `std::byte` example in a quick godbolt snippet and MSVC wouldn't compile without adding /std:c++17, because of course it defaults to earlier. Which is silly, but that's also the story of my life.

And don't get me wrong - that's all relatively minor - but it's all for middling to negative value IME. `void*` is frequently clearer - it's a signal that it's an opaque blob at this point in the code, and that something else will try to give it meaning later. I struggle to think of a single bug that I've encountered, that would've been caught by the compiler had I used `std::byte` over `unsigned char` or `void`. And conversely, I've seen APIs accepting `std::byte` but requiring higher alignment, where with `void` I might not have dropped my guard as much.

> `std::span`

At least manages to bind pointer and size into a single variable, which IME at least has the advantage of eliminating some bugs (e.g. mismatching pointers and sizes) and allowing some nifty utility functions to become a lot more wieldy. You can do things like feed it an array and not have to do any of your own `sizeof(...)` shenannigans. At this point you're possibly getting into positive expected value, but I'm going to eye roll at pull requests refactoring `void*` based stuff to use it unless I see at least one actual concrete example of calling code improving alongside it - I don't want just hypothetical theoretical ergonomics, I want actual concrete ergonomics!

[AnimalMuppet]

> `void*` is frequently clearer - it's a signal that it's an opaque blob at this point in the code, and that something else will try to give it meaning later.

And that's fine, until something else gives it the wrong meaning later. If you're just plumbing, and you're pumping around opaque blobs, if somewhere in the plumbing you connect the wrong source to the wrong destination, you get no warning.

[ryandrake]

Yes, in this case, void* is kind of smelly. If the intent of your function is to receive a const struct MyCustomData*, then that should be the type of the argument. If you later need to handle a const struct MyOtherCustomData*, you can add an overload that takes that argument. Or use a template as others pointed out. Use the type system to help you, so you're warned if you try to pass the method const struct BadCustomData* by accident.

If you truly don't know what the underlying structure of the "blob" of data is, sure, go ahead and use void* and explicitly convert the pointer type when you know what it is, but at least add a comment that you're entering the danger zone.

[MaulingMonkey]

To be fair, the `void*` is already a pretty big hint that you're in the danger zone.

[MaulingMonkey]

> if somewhere in the plumbing you connect the wrong source to the wrong destination, you get no warning.

A valid concern. I've been in the position of having to fix those bugs.

I'm not going to recommend `qsort` over `std::sort` or anything like that. I've seen `void*` "user data" pointers in C APIs and decided to stuff runtime checkable handle values in there instead of real pointers to blobs. In Rust, this can mean avoiding some unnecessary `unsafe { ... }` blocks, since while reading anything from a `*const c_void` requires such things, reading from a global `Mutex<HashMap<*const c_void, Arc<dyn Any>>>` or similar nonsense does not. I'll eat the performance hit unless I'm worrying about an actual hot path!

And I'm not going to stand in the way of newtype wrappers around void pointers either. I'll +1 the PRs with `class ASpecificKindOfBlob { void* data; size_t length; };` and suchlike as well, if `std::span`s aren't your type of thing, and abide by measures to centralize such plumbing in one place such that the opportunities to make a mistake are fewer.

But sometimes a blob is just a blob, and breaking out `std::byte` is putting lipstick on a pig. And it's not even the right color lipstick.

[account42]

> and the latter is a whole damn enum class with a strange adversion to arithmetic, where `byte |= 1` becomes `byte |= std::byte(1)`, `byte += 1` becomes `byte = std::byte(std::to_integer<std::uint8_t>(byte) + 1);`, and both become something you can accidentally step into in your full debug builds because it's an actual function call (at least on MSVC - still extra instructions on clang/gcc, but I can see the dang call instruction on MSVC!) instead of a compiler built in.

That's the point, std::byte is for opaque bytes. You're not expected to do arithmetic directly just like you can't do arithmetic on void.

[MaulingMonkey]

> That's the point, std::byte is for opaque bytes. You're not expected to do arithmetic directly just like you can't do arithmetic on void.

That'd make a whole lot more sense to me if `std::byte` didn't explicitly implement a whole bunch of bit twiddling operations:

    << >> |= &= ^= | & ^ ~

This isn't opaque. This is a poor man's half-assed `std::bitset<8>` with a guaranteed `sizeof(std::byte) == 1`.

[drivebyhooting]

Span will increase compilation time for no useful reason. It’s not any safer at the call site.

[ndiddy]

Span lets you use a ranged for loop to iterate over the contents without worrying about exceeding the bounds, which is safer than pointer+size if that's all you'll be doing. C++26 also introduces .at() for span, and the new hardened standard library enforces bounds checking when using operator [] on a span.

[drivebyhooting]

The caller still needs to construct the span correctly.

[ndiddy]

You can pass both C arrays and some STL containers (i.e. std::vector, std::array) into a function that takes a span, and the span will get constructed automatically. You have to construct it manually if all you have is a pointer and a length, but I don't know what you'd expect to happen there.

[drivebyhooting]

It’s not semantically safe to pass arbitrary vectors into a generic buffer copying function. The T in a vector<T> could have internal pointers or worse things.

Either the objects are simple and trivially copiable, or you need a proper serialization library.

Sure you can use span to generalize slides and iteration, but I don’t think that’s the point of the article.

[fluffybucktsnek]

In comparison to a plain void* and a separate size, it's still an improvement. As others mentioned, void* suffers from the same problem (it might point to a type that is not trivially copyable), except it has more opportunities for mistakes.

In contrast, with span, you can instantiate only to span<uint_8> (or something similar) and you'd still be able to accept other buffer types (such as vector<uint_8>, array<uint_8>, etc.). Alternatively, you can make T bounded to be trivially copyable. You can't do that with void*.

[throwaway27448]

Well if compilation time is an issue, you chose the worst possible language to use. But if you must use C++, you should use the mechanisms that best communicate intent.

[drivebyhooting]

It’s this kind of attitude that perpetuates bad compilation time.

Templates have to get parsed and instantiated over and over again. Then you need link time optimization to deduplicate all the redundant copies of the same code.

[fluffybucktsnek]

If youif you are using C++, your last concern will be compilation times. By this point, just use C.

[drivebyhooting]

Untrue. Lots of effort is spent optimizing compilation time at big FAANG companies. And there a lot of established techniques for creating “compiler firewalls” and explicitly instantiating templates once.

[fluffybucktsnek]

But these compilation times optimizations don't significantly undermine the other goals. Given that we're talking about std::span<T>, a pretty small template all things considered, I think practical evidence (e.g. actual cases) of impact is needed.

[pjmlp]

No they don't, modules exist, as do external template libraries.