Biggest open question is whether the small changes to the module system in this standard will actually lead to more widespread adoption
Biggest open question is whether the small changes to the module system in this standard will actually lead to more widespread adoption
The best thing the C++ WG could do is to spend an entire release cycle working on modules and packaging.
It's nice to have new features, but what is really killing C++ is Cargo. I don't think a new generation of developers are going to be inspired to learn a language where you can't simply `cargo add` whatever you need and instead have to go through hell to use a dependency.
To me, the most important feature of Cargo isn't even the dependency management but that I don't ever need to tell it which files to compile or where to find them. The fact that it knows to look for lib.rs or main.rs in src and then recursively find all my other modules without me needing to specify targets or anything like that is a killer feature on its own IMO. Over the past couple of years I've tried to clone and build a number of dotnet packages for various things, but for an ecosystem that's supposedly cross-platform, almost none of them seem to just work by default when I run `dotnet build` and instead require at least some fixes in the various project files. I don't think I've ever had an issue with a Rust project, and it's hard not to feel like a big part of that is because there's not really much configuration to be done. The list of dependencies is just about the only thing in there that effects the default build; if there's any other configuration other than that and the basic metadata like the name, the repo link, the license, etc., it almost always will end up being specifically for alternate builds (like extra options for release builds, alternate features that can be compiled in, etc.).
Yep ... go/zig pkg management has the same benefit compared to c/c++.
> The fact that it knows to look for lib.rs or main.rs in src and then recursively find all my other modules without me needing to specify targets or anything like that is a killer feature on its own IMO.
In the interest of pedantry, locating source files relative to the crate root is a language-level Rust feature, not something specific to Cargo. You can pass any single Rust source file directly to rustc (bypassing Cargo altogether) and it will treat it as a crate root and locate additional files as needed based on the normal lookup rules.
For me the lack of dependency hell until I hit a c/c++ component somewhere in the build is the real winner.
I’m still surprised how people ignore Meson. Please test it :)
https://mesonbuild.com/
And Mesons awesome dependency handling:
https://mesonbuild.com/Dependencies.html
https://mesonbuild.com/Using-the-WrapDB.html#using-the-wrapd...
https://nibblestew.blogspot.com/2026/02/c-and-c-dependencies...
I suffered with Java from Any, Maven and Gradle (the oldest is the the best). After reading about GNU Autotools I was wondering why the C/C++ folks still suffer? Right at that time Meson appeared and I skipped the suffering.
Feel free to extend WrapDB.Meson is indeed nice, but has very poor support for GPU compilation compared to CMake. I've had a lot of success adopting the practices described in this talk, https://www.youtube.com/watch?v=K5Kg8TOTKjU. I thought I knew a lot of CMake, but file sets definitely make things a lot simpler.
Meson merges the crappy state of C/C++ tooling with something like Cargo in the worst way possible: by forcing you to handle the complexity of both. Nothing about Meson is simple, unless you're using it in Rust, in which case you're better off with Cargo.
In C++ you don't get lockfiles, you don't get automatic dependency install, you don't get local dependencies, there's no package registry, no version support, no dependency-wide feature flags (this is an incoherent mess in Meson), no notion of workspaces, etc.
Compared to Cargo, Meson isn't even in the same galaxy. And even compared to CMake, Meson is yet another incompatible incremental "improvement" that offers basically nothing other than cute syntax (which in an era when AI writes all of your build system anyway, doesn't even matter). I'd much rather just pick CMake and move on.
Build system generators (like Meson, autotools, CMake or any other one) can't solve programming language module and packaging problems, even in principle. So, it's not clear what your argument is here.
> I’m still surprised how people ignore Meson. Please test it :)
I did just that a few years ago and found it rather inconvenient and inflexible, so I went back to ignoring it. But YMMV I suppose.
> After reading about GNU Autotools
Consider Kitware's CMake.
Agreed, arcane cmake configs and or bash build scripts are genuinely off-putting. Also cpp "equivalents" of cargo which afaik are conan and vcpkg are not default and required much more configuring in comparison with cargo. Atleast this was my experience few years ago.
It's fundamentally different; Rust entirely rejects the notion of a stable ABI, and simply builds everything from source.
C and C++ are usually stuck in that antiquated thinking that you should build a module, package it into some libraries, install/export the library binaries and associated assets, then import those in other projects. That makes everything slow, inefficient, and widely dangerous.
There are of course good ways of building C++, but those are the exception rather than the standard.
"Stable ABI" is a joke in C++ because you can't keep ABI and change the implementation of a templated function, which blocks improvements to the standard library.
In C, ABI = API because the declaration of a function contains the name and arguments, which is all the info needed to use it. You can swap out the definition without affecting callers.
That's why Rust allows a stable C-style ABI; the definition of a function declared in C doesn't have to be in C!
But in a C++-style templated function, the caller needs access to the definition to do template substitution. If you change the definition, you need to recompile calling code i.e. ABI breakage.
If you don't recompile calling code and link with other libraries that are using the new definition, you'll violate the one-definition rule (ODR).
This is bad because duplicate template functions are pruned at link-time for size reasons. So it's a mystery as to what definition you'll get. Your code will break in mysterious ways.
This means the C++ committee can never change the implementation of a standardized templated class or function. The only time they did was a minor optimization to std::string in 2011 and it was such a catastrophe they never did it again.
That is why Rust will not support stable ABIs for any of its features relying on generic types. It is impossible to keep the ABI stable and optimize an implementation.
> C and C++ are usually stuck in that antiquated thinking that you should build a module, package it into some libraries, install/export the library binaries and associated assets, then import those in other projects. That makes everything slow, inefficient, and widely dangerous.
It seems to me the "convenient" options are the dangerous ones.
The traditional method is for third party code to have a stable API. Newer versions add functions or fix bugs but existing functions continue to work as before. API mistakes get deprecated and alternatives offered but newly-deprecated functions remain available for 10+ years. With the result that you can link all applications against any sufficiently recent version of the library, e.g. the latest stable release, which can then be installed via the system package manager and have a manageable maintenance burden because only one version needs to be maintained.
Language package managers have a tendency to facilitate breaking changes. You "don't have to worry" about removing functions without deprecating them because anyone can just pull in the older version of the code. Except the older version is no longer maintained.
Then you're using a version of the code from a few years ago because you didn't need any of the newer features and it hadn't had any problems, until it picks up a CVE. Suddenly you have vulnerable code running in production but fixing it isn't just a matter of "apt upgrade" because no one else is going to patch the version only you were using, and the current version has several breaking changes so you can't switch to it until you integrate them into your code.
It's not true that Rust rejects "the notion of a stable ABI". Rust rejects the C++ solution of freeze everything and hope because it's a disaster, it's less stable than some customers hoped and yet it's frozen in practice so it disappoints others. Rust says an ABI should be a promise by a developer, the way its existing C ABI is, that you can explicitly make or not make.
Rust is interested in having a properly thought out ABI that's nicer than the C ABI which it supports today. It'd be nice to have say, ABI for slices for example. But "freeze everything and hope" isn't that, it means every user of your language into the unforeseeable future has to pay for every mistake made by the language designers, and that's already a sizeable price for C++ to pay, "ABI: Now or never" spells some of that out and we don't want to join them.
I would suggest importing binaries and metadata is going to be faster than compiling all the source for that.
"That makes everything slow, inefficient, and widely dangerous."
There nothing faster and more efficient than building C programs. I also not sure what is dangerous in having libraries. C++ is quite different though.
Of course there is. Raw machine code is the gold standard, and everything else is an attempt to achieve _something_ at the cost of performance, C included, and that's even when considering whole-program optimization and ignoring the overhead introduced by libraries. Other languages with better semantics frequently outperform C (slightly) because the compiler is able to assume more things about the data and instructions being manipulated, generating tighter optimizations.
>There are of course good ways of building C++, but those are the exception rather than the standard.
What are the good ways?
Build everything from source within a single unified workspace, cache whatever artifacts were already built with content-addressable storage so that you don't need to build them again.
You should also avoid libraries, as they reduce granularity and needlessly complexify the logic.
I'd also argue you shouldn't have any kind of declaration of dependencies and simply deduce them transparently based on what the code includes, with some logic to map header to implementation files.
"Do not do it" looks like the winning one nowadays.
In my experience, no one does build systems right; Cargo included.
The standard was initially meant to standardize existing practice. There is no good existing practice. Very large institutions depending heavily on C++ systematically fail to manage the build properly despite large amounts of third party licenses and dedicated build teams.
With AI, how you build and integrate together fragmented code bases is even more important, but someone has yet to design a real industry-wide solution.
Speedy convenience beats absolute correctness anyday. Humans are not immortal and have finite amount of time for life and work. If convenience didn't matter, we would all still be coding in assembly or toggling hardware switches.
C++ builds are extremely slow because they are not correct.
I'm doing a migration of a large codebase from local builds to remote execution and I constantly have bugs with mystery shared library dependencies implicitly pulled from the environment.
This is extremely tricky because if you run an executable without its shared library, you get "file not found" with no explanation. Even AI doesn't understand this error.
The Mars Polar Lander and Mars Climate Orbiter missions would beg to differ.
(And "absolute" or other adjectives don't qualify "correctness"... it simply is or isn't.)
I didn’t think header only was that bad - now we have a nightmare of incompatible standards and compilers.
No, because most major compilers don't support header units, much less standard library header units from C++26.
What'll spur adoption is cmake adopting Clang's two-step compilation model that increases performance.
At that point every project will migrate overnight for the huge build time impact since it'll avoid redundant preprocessing. Right now, the loss of parallelism ruins adoption too much.
No. Modules are a failed idea. Really really hard for me to see them becoming mainstream at this point.
The idea is great, the execution is terrible. In JS, modules were instantly popular because they were easy to use, added a lot of benefit, and support in browsers and the ecoysystem was fairly good after a couple of years. In C++, support is still bad, 6 years after they were introduced.
Exactly. C++ is still waiting for its "uv" moment, so until then modules aren't even close to solved.
And uv required some ground work, where the PEP process streamlined how you define a python project, and then uv could be built on top.
No idea if modules themselves are failed or no, but if c++ wants to keep fighting for developer mindshare, it must make something resembling modules work and figure out package management.
yes you have CPM, vcpkg and conan, but those are not really standard and there is friction involved in getting it work.
Much like contracts--yes, C++ needs something modules-like, but the actual design as standardized is not usable.
Once big companies like Google started pulling out of the committee, they lost their connection to reality and now they're standardizing things that either can't be implemented or no one wants as specced.
I emphatically agree. C++ needs a standard build system that doesn’t suck ass. Most people would agree it needs a package manager although I think that is actually debatable.
Neither of those things require modules as currently defined.
Can you explain why you think modules are a failed idea? Because not that many use them right now?
Personally I use them in new projects using XMake and it just works.
I'm not the PC but I think you miss most of the pain points due to: 'personal' projects.
There's not a compatible format between different compilers, or even different versions of the same compiler, or even the same versions of the same compiler with different flags.
This seems immediately to create too many permutations of builds for them to be distributable artifacts as we'd use them in other languages. More like a glorified object file cache. So what problem does it even solve?
Because as a percentage of global C++ builds they’re used in probably 0.0001% of builds with no line of sight to that improving.
They have effectively zero use outside of hobby projects. I don’t know that any open source C++ library I have ever interacted with even pretends that modules exist.
"Failed idea" gives modules too much credit. Outside old codebases, almost no one outside C++ diehards have the patience for the build and tooling circuss they create, and if you need fast iteration plus sane integration with existing deps, modules are like trading your shoes for roller skates in a gravel lot. Adopting them now feels like volunteering to do tax forms in assembbly.
I frankly wish we'd stop developing C++. It's so hard to keep track of all the new unnecessary toys they're adding to it. I thought I knew C++ until I read some recent C++ code. That's how bad it is.
Meanwhile C++ build system is an abomination. Header files should be unnecessary.