[lallysingh]

Wow this got really long. I was one of the coauthors for a reflection proposal (N3340) over a dozen years ago. Implementing compile-time reflection is honestly trivial - you basically transfer data from the symbol table on-demand into template specializations. It was roughly 1500 LOC to modify g++ to do it.

Looking at the examples (https://isocpp.org/files/papers/P2996R4.html#examples) what really stands out is the direct integration of type-syntax into the language. It fits in with a certain token-substitution way that connects back to templates. It also replaces some of the uglier operators (typeof?).

I hope it goes int! During the language's stagnation I left for a while, perhaps it'll be competitive again soon.

[cb321]

I think another good example might be extracting function signatures (parameter names & types, default values -- if any) at compile-time for various purposes.

[stiglitz]

By ”stagnation” do you mean “not getting new features”?

[CuriousCosmic]

C++ has gotten a ton of quality of life features with each update. The issue is less that new features aren't coming and more that new features bake through countless iterations of proposals for close to or often over a decade until everyone in WG21 is happy.

So it's not that we aren't getting features. They are coming quite fast and people regularly complain that new C++ has too many things for them to learn and keep up with. The issue is that those are the same features everyone has been asking for for over a decade so the people that really care found workarounds and eventually move over to the new std way of doing things when they can while everyone else continues waiting for that one feature they really care about.

[maccard]

Also that the features c++ is getting are bolt on additions that we already have solutions for. I think fmt is a great example - fmt is a header only library that can be dropped in. Meanwhile std format was standardised without printing to stout. That took 3 years to standardise. Meanwhile we’re working on things like ranges, and instead of implementing them in the language it’s shoe horned in as a library feature - we now pay massive compile time hits for these features that are being shoved in alongside the kitchen sink. Meanwhile the solution (modules) has been talked about longer than I’ve been writing c++, it’s still unusable, and it hasn’t shown one of the key things people have been begging for for a decade - faster compile times.

I think the committee is focused on the wrong things

[meindnoch]

>instead of implementing them in the language it’s shoe horned in as a library feature

Quite the opposite. Proliferating the language itself with ad-hoc constructs would be shoe-horning.

[maccard]

I disagree completely. Libraries like ranges are dumped into algorithm, and are de-facto considered parts of the language. Reflection has gone back to have range support added, for example. Another one is that span has a performance overhead due to it being implemented as a normal type. If it was part of the language rather than a library type, the compiler could make assumptions about it, but instead it’s treated equivalent to me writing it myself. I would much rather gcc saw me passing a span around and could treat it as a special built in type.

[meindnoch]

>Another one is that span has a performance overhead due to it being implemented as a normal type. If it was part of the language rather than a library type, the compiler could make assumptions about it, but instead it’s treated equivalent to me writing it myself.

False. Nothing prevents compilers from giving their own stdlib types special treatment under the hood.

[VHRanger]

You can't have faster compile times. If you want fast compile times C++ needs to sacrifice something else (ABI compatibility, compatibility to compile code from 1979 for some dead big endian 12-bit word chip, etc.

In fact the truth is the people working on C++ don't actually value fast compile times over other matters (fast runtime, ABI compatibility, etc.)

They say they do. But they don't in their actions.

One egregious example: look at the compilation speeds of clang with release build configs (-O2 or higher, etc.) over the years.

It compiles much slower now than it did in 2014 for the same code. The compilation speed is worsening at a much faster rate than the runtime speeds are improving from version to version.

[maccard]

I agree with you. I would move heaven and earth for faster unoptimizrd builds, but I’m perfectly happy with multi hour O2 builds from clang. The state that modules was standardised in proved what you’re saying - there were many opportunities to allow for faster compile times but instead we chose maximum flexibility with no consideration for what that leaves on the table.

[pjmlp]

That sacrifice is called C++20 modules and quite alright on VC++ and clang 18.

[lallysingh]

Ha! Modules. I wrote a basic version of that in 2006 for Boost. This is as big a useless mess as web components. It feels like c++ is in the legacy category with x86, still here, tolerable due to exponential efforts, and still dying for simpler solutions that aren't beholden to decades-old design mistakes. (variable instruction width, context-sensitive grammar, #include model, etc).

[maccard]

I think that what we have standardised as modules give us a path off the include model, honestly. It’s just that it’s the most pandered-to version of modules you could imagine. We entirely changed the compilation model and didn’t manage to tie module names to filesystem paths, meaning you need to parse the module file to figure out what module it is. It’s death by a thousand cuts

[account42]

Personally I'd rather the comitte take longer and require more implementation experience before accepting new features. There are still too many half-baked ideas that turn out to be mistakes afterwards, resulting in either needless breaking changes or being stuck with bad solutions.

This is especially true for library features where users can always use third party libraries for containers/algorithms that are yet to be standardized (or indifinitely - not everything should be added to the stdlib). But even language features can and should exist as compiler extensions before we are stuck with them.

[gpderetta]

Failed library features at least can be relatively easily deprecated, forgotten and left to rot on the side. Language features will bloat the language almost forever.

One nice advantage of static reflection, macros and other form of program synthesis is that you can experiment with new syntax as a library before committing to integrating it to the base language.

[chipdart]

> There are still too many half-baked ideas that turn out to be mistakes afterwards (...)

Care to point an example?

[gpderetta]

Some examples on top of my mind:

- export templates is the canonical one.

- Universal references are a great feature in principle, but the way they are integrated in the language is far from ideal.

- Both features are great in isolation, but the interaction between initializer lists and aggregate initialization is a giant footgun.

- Coroutines are overly complex and still incomplete but I still have hope.

- Modules feel DOA so far.

- Unrestricted compile time evaluation is great, but the constexpr qualifier per se doesn't guarantee any useful property.

edit: overall I'm happy with the evolution of the language, but the standardization process has flaws

[pjmlp]

Module are already being used by Office, and those of us that don't need to rely on GCC, don't hate CMake, can already enjoy using them.

Which is what I have been using on my C++ hobby projects for the last two years, on work projects we are still on C++17 land anyway.

[kragen]

marshall cline's c++ mini-faq is a list of about 100 pages of them from the 01990s

[chipdart]

> marshall cline's c++ mini-faq (...)

Published in 1994.

Literally 30 years ago, years before there was even anything resembling a C++ standard.

I'm not sure why you thought it's relevant.

[physicsguy]

> the people that really care found workarounds

Or stopped writing C++, I'd consider myself one of these for many use cases I used to use it for.

[chipdart]

> Or stopped writing C++, I'd consider myself one of these for many use cases I used to use it for.

Some use cases like GUI programming sound like they are better addressed by specialized tech stacks. Nevertheless, either you're talking about greenfield projects or you are hard pressed to find a justification to rewrite a project in another framework. Claiming you stopped writing C++ doesn't fit the bulk of the experience of anyone maintaining C++ projects.

[PathOfEclipse]

My experience maintaining old codebases is that you are just as hard-pressed to find a justification to write code to use new language features, or even to take the time to upgrade the language and compiler version. Most often you just continue writing code in the same style as the rest of the code base using an old version of the language and runtime.

[chipdart]

> My experience maintaining old codebases is that you are just as hard-pressed to find a justification to write code to use new language features, or even to take the time to upgrade the language and compiler version.

That's perfectly fine. You should only pay for what you use.

Your average project, however, consumes dependencies and needs to keep them updated. Just because the code you write doesn't use them that doesn't mean your dependencies don't. So everyone still benefits with each release of C++ even if the are not using fancy features.

[physicsguy]

Yes that's right, what I meant was that for many of the use cases on greenfield projects that I used to use C++ for, I no longer do.

[lallysingh]

Services get split up and some parts rewritten. The parts are often written in new languages.

[Grayskull]

> They are coming quite fast and people regularly complain that new C++ has too many things for them to learn and keep up with.

I never got this. Can't you just decide to use subset of the language? No-one forces people to use every single feature. It's okay to use C++ like "C with classes" and occasionally cool new thing, when it is right tool for the job. Only people where this argument is truly valid are compiler/tools people.

[usrnm]

> Can't you just decide to use subset of the language?

No, you can't. Not in the long run, at least. You will have to use libraries that have chosen a different subset, new people will join your team, things will get sloppy as the company grows, etc. Committing to a subset of the language is not free, it's hard and it's a lot of work. And for what?

[bluGill]

> Can't you just decide to use subset of the language?

That is harder than it sounds. First you have to select which subset to use, it is almost impossible to get any two engineers to agree on that - if you do get agreement that is a bad sign - generally it means the people in the room don't know C++ well enough to make the decision and so you choose the wrong one. The best you can hope for is a compromise where nobody is happy - and thus everyone will look for an excuse to bring in their pet part of C++ not in the subset because there is a "good reason" for an exception.

Even if you select a subset it is almost impossible to enforce whatever subset because even if you don't allow your people to use it directly odds are you bring in a third party library that does use it (the C++ standard library being the big one!)

There are a few exceptions to the above. No exceptions/no RTTI are commonly disabled exceptions and so you will get some compiler and library support. Game companies commonly write their own standard library. Both of these are done for performance reasons and have specific domain specific reasons that can be validated in a profiler to set their rules.

Not related to reflection, but C++26 is also likely to get profiles which will disable specific old constructs, (new/delete) which are proven to be error prone and thus result in security issues. These are a good subset to use, but it is about security and so mostly doesn't get the types of subsets you are talking about.

[CuriousCosmic]

You can still enforce a style guide and limit certain constructs via code review.

Plenty of the modern C++ people already do this by enforcing things like "no raw loops", "no raw pointers", or "no raw synchronization primitives" during code review.

The issue is that it's a lot harder to justify avoiding new features than it is to justify avoiding old features unless you have a tooling specific reason (ex lack of support) to do so.

[bluGill]

> during code review.

There is the problem - code reviews are done by humans and so it is really easy to read some code and not think "wait this is new code it can't do that anymore". I read a lot of old code as part of my job and it often isn't worth the bother to update working code to new standards.

> it's a lot harder to justify avoiding new features than it is to justify avoiding old features

The problem is the opposite - people keep using old features when the new is better. I realize not everything new is better, but most of them are, yet people keep refusing to learn and use the new thing without good justification.

[CuriousCosmic]

Personally I think this is true. C++ is multi paradigm and can be effectively used with many different subsets of the language and those subsets still interact well.

However that opinion is kind of a minority. There are a lot of people in the community who don't want to have to learn new features just because a dependency happens to use/expose them. I don't personally see the issue with it.

I'd rather learn std features any day over non-std features. It's just a better use of my time because they work everywhere and someday I might need them. However again not everyone shares this opinion.

[lallysingh]

For 1 person, sure. The larger the team, or the more teams involved, this drops from easy to completely impossible.

[kragen]

or people who need to maintain someone else's code, debug their own, write a library someone else might use, or understand compiler error messages, all of which involve understanding language features you don't yourself use (at least intentionally)

[AnimalMuppet]

Partly true.

If you're writing library code that someone else might use, you don't have much need to understand the features you don't use, unless you have to handle them at the interface. If you're debugging your own code, you really shouldn't have to understand features that you didn't use. (Mostly - see the next paragraph.)

You did say "intentionally". You could wind up using a feature unintentionally, but it's not very common, because most of the new features are either in a new library (which you have to explicitly call), or a new syntax. There are definitely exceptions - I could easily see you using a move constructor without meaning to.

Maintaining someone else's code... yeah. You have to understand whatever they used, whether or not it made any sense for them to use.

[kragen]

i accidentally used the new implicit constructors for aggregates in c++ the other day, and then my code didn't compile with the version of clang i have installed on my cellphone

[foldr]

Not really. Even parts of the standard library (e.g. std::variant) more or less require the use of quite advanced language features.

[adrianN]

The people complaining and the people asking for features need not be overlapping sets.

[lenkite]

Wish C++ fixed some of its mistakes in the standard library. std::regex is embarrassing when even Python can beat it and nobody uses std::unordered_map due to its pointer chasing. Basic Maps are something that you shouldn't need to use a third party library for.

[ghosty141]

Could you explain the issue with unordered_map?

[lenkite]

The standard guarantees that you can get a pointer to an object in the map and this pointer will remain valid after rehashing and insertion/deletion of other elements. That basically forces implementers to use “buckets with linked lists”, also known as separate chaining. This is not cache friendly (and also suffers from excessive allocation). Other hash map implementations like abseil's don't provide this guarantee so they can put everything right there inline, which is much more efficient.

[okanat]

I think the bureaucratic cadence of the things also make C++ not a unified entity. C++ is patchwork language. So many of the new features don't work well together or don't fit together or they have conflicting goals.

Since the proposals target problems with differing philosophies, they each have different traps in them from bad time complexity to outright unrefined behavior. Keeping up with the updates hard because of this.

I think many C++ projects are (or will be) basically infeasible to maintain not because of the old problems but due to the exploding complexity of the interactions of all features, unless developers actively ban using large parts of the language.

[CuriousCosmic]

> C++ is patchwork language. So many of the new features don't work well together or don't fit together or they have conflicting goals.

I don't really see this as true. In my experience most C++ features actually "just work" together and there are relatively few footguns involved in mixing features.

And it's less that C++ is a patchwork language and more that it is multi-paradigm and multi-discipline. Some features have specific applications and they get used inappropriately but in my experience that is solved with a quick reference/citation of the standard during code review or in a new ticket.

[vlovich123]

N3340 is from 2011. Prior to c++11 they had failed to deliver major changes to the language. And arguably the disfunction is still there where big ideas get destroyed in committee (reflection) or take forever and come out half-baked (modules).

[rerdavies]

Speaking of half-baked, did continuations get fixed?