As someone who writes high-reliability C++ but is completely outside the standards process, I see the issues with C++ Contracts. It isn’t clear that it solves a problem that anyone has in real codebases, especially after C++20 concepts.
If you were already writing high-reliability C++ then the benefits are difficult to quantify. If you weren’t writing high-reliability C++ then it saves you almost nothing over doing the standard idioms of high-reliability C++ that were already available to you at very marginally more cost. It does standardize expression of it in narrow cases but the payoff seems minimal.
Most of what C++ Contracts delivers is a mashup of what you can already do with constexpr and C++20 Concepts. I like reliability features but this feature, as delivered, looks fairly useless if you already use reliability features. A compelling standard would need to make much deeper guarantees out of the box. And the compiler can already see through most compositions of constexpr and C++20 concepts, which is already very expressive.
C++ Contracts looks a bit like a feature that was designed long before current standard features existed.
C++ concepts evaluate the properties of types at compile-time. You can inject arbitrary constraints on type properties anywhere in the code including conditional codegen. It is a way of asking if a type “can express this complex set of abstract things or has this enumerated set of properties” with almost arbitrary detail. They are extremely powerful in terms of expressiveness and specialization of code. Insanely good for performance and reliability engineering.
One of the best features to be added to C++ in many years.
C++ contracts are an attempt to bring C asserts into the C++ age. The weakness of C++ contracts is that they are mostly syntactic sugar over C asserts. If you really care about this type of thing, you probably already have a custom C++ assertion framework that is at least as capable if not more.
The promise of C++ contracts is that they can aid formal verification, which would be great. As delivered, it can’t do much more than was already possible, which will inhibit adoption.
I maintain a codebase that I’ve migrated from C++98 to C++11 and all the way to C++23 and even a bit of draft 26 (the latter for some minor library improvements). Few things made me quite as happy as moving from using SFINAE to using requires clauses and concepts.
(IMO the single best improvements over the years have been atomics and maybe variadic templates.)
I think you are right to position atomics and variadic templates as among the most consequential features of C++ in the last couple decades. It made an enormous number of things possible.
One thing I give the C++ feature gods credit for is recognizing material deficiencies in systems languages and unapologetically trying to fill those gaps starting with C++11. The addition of atomics, strict variadics, constexpr, lambdas, concepts, lifetime annotations, etc has been transformative for C++.
The weakness of C++ contracts is that they are mostly syntactic sugar over C asserts.
The sugar is actually one of my issues with them. The evaluation semantics are much more complicated / potentially slower than C asserts because of the sugar, and why you would have to pay those costs isn't obvious at first glance. Lisa Lippincott's excellent talk on the design of contracts [0] is what switched me from a sort of neutral support to disliking it. I think it's a stupid place for the national bodies to draw the line though. std::regex is acceptable, but a nothingburger like contracts tanks the vote?
To be clear, I have a lot of issues with the contracts proposal. I probably wouldn’t use despite living out on the standards frontier. I don’t even use C asserts already because they are not expressive enough in important ways. This proposal kind of reifies the inadequacies.
I think the risk is that C++ contracts become an evolutionary dead-end that hang around forever in code bases because they were standardized. It wouldn’t be the first time this has happened.
Huh? Concepts are types of types. Contracts are fancier, structured runtime assertions. What does one have to do with the other? They're nothing alike.
They both start with the letter C, have two syllables, and have/had a hard time getting into the standard. If you’re not paying close attention, it’s easy to get them confused.
I don't buy the idea that in "high-reliability C++" every condition worth checking can be checked statically, not unless you define "high-reliability" vacuously as that set of programs for which the claim is true. Real-world programs have legitimate reasons to verify invariants dynamically, and C++26 contracts provides an improved way to do so.
While the C++26 variant of contracts doesn't provide the benefits of its static-analysis-centric ancestor from 2014, and therefore isn't as consequential a feature, it still provides value to some and is absolutely not important enough to be worth killing a standard. Concepts do not provide this value.
In any case, it's simply false that C++26 contracts are unnecessary because we have concepts, yet this claim is the thrust of your initial comment.
> While the C++26 variant of contracts doesn't provide the benefits of its static-analysis-centric ancestor from 2014
Do you have any information as to why they shifted the focus from static analysis to runtime checks? I only remember that it was based on some Microsoft annotation language or something.
> The problem is that a bunch of people who didn't care for them did something very extreme by voting against approving C++26.
The only extreme and tone deaf thing I see in this story is how contracts proponents were faced with multiple papers demonstrating quite clearly and extensively how they were broken in specification and in form, but still tried to ignore all the criticism and force them through a consensus process in spite of being clearly opposed.
How does this make any sense? What was the plan here? To blackmail the C++ community to accept a broken feature under threat of the proposal not passing?
Make it make sense?
What I want to see is the people who tried to force contacts upon the process in spite of all opposition to come forth and explain their rationale. It was highly absurd and even unthinkable to force a broken feature down C++'s throats with bureaucratic chicanery, and then complain that the same bureaucracy has mechanisms to stop it's abuse. I for one would like to hear an explanation.
This article makes it sound the options are normally approval, rejection and abstention, but that this time round a fourth option, "disapproval", was reached. It that the case, or are they just trying to say that people rejected it?
While I can understand that C++ contracts were met with controversy, contract annotations scoped at analysis time that can be verified by external tools, such as static analyzers, model checkers, or automatic theorem provers, are incredibly useful.
I put together an alternative function contract and invariant mechanism in C using CBMC and custom macros that effectively allows me to perform formal methods in C using compositional verification. The reason why I chose C is because of its relative simplicity and relative ease of building tooling around it. C++ contracts provide some feature parity, and would let me take advantage of some of the features in C++ relative to C.
I hope that the contract proposal is workshopped and simplified so it can be proposed again for a future version. Its current form is unsuitable, but it deserves a second chance with a simpler implementation. Contracts would narrow the safety gap between C++ and languages such as Ada / SPARK.
Contracts are useful, but don't guaranteed anything if type safety & memory safety can be bypassed.
I think the ISO panel made the right call. The real world consider memory safety & execution integrity to already be critical issues (and C++ no longer to be viable), and they are correct. The WG has its priorities wrong.
I get why some folks would like to see contracts in the language, but C++ is also buckling due to the shear complexity that's getting tacked on to it. I'd rather see more proposals such as C++26's "erroneous behavior" that attempts to reign in the language's shortcomings.
Agree. There's an argument that Contracts reduces the complexity of using the language because it offers a more readable alternative to template metaprogramming (also, it has better error messages). But the argument really falls apart when you review WG21's track record for other features.
Like for example, Coroutines were billed as an easier way to write concurrent code, but personally I think it completely failed and ended up being hopelessly complex and confusing. Modules are the same - superficially they make things simpler, but when people actually go to adopt it, the details are so complex that nobody bothers.
> There's an argument that Contracts reduces the complexity of using the language because it offers a more readable alternative to template metaprogramming
Like most people in this thread, you should really read up on contracts before commenting. The contracts proposal is for runtime assertions, and their problem is that they are poorly specified and fundamentally broken. Their proponents haven't been addressing any of their concerns and tried to push a half baked version of them down everyone's throats, which was why they failed to pass.
Who cares about the ABI when the current ABI has a bunch of bad issues with it. For any backwards compatibility thing there is always AI that can rewrite old code.
As an avid non-C++ programmer, can I suggest doing something about the build/module system? I shouldn't have to learn a separate language (CMake) and figure out the right include files to pull in a library.
I mean, I mainly say this to joke because it's probably unfixable at this point, but whenever I mess with it, I'm struck by how hard/opaque C++ makes this problem compared to most other languages.
There is no standard build/module system or way of dependency management. Unfortunately, this is because there's no standard compiler with standardized flags so C++ would also have to standardize compiler behaviour too.
Large FAANGs that would be incentivized to change it don't care because they have their own in-house C++ build systems like bazel (Google) or buck2 (Meta) that are far faster than cmake (distributed compilation and caching) but require huge teams to maintain. Unfortunately, this distributed compilation and caching layer is something that many other languages don't have since their build systems are made for single devs building locally.
Also the dependencies can be added in a myriad of ways. Your build system can download them, your meta-build dependency manager can find them (Conan), your Linux distro can provide them (system libraries), or maybe you just download an object file from a website + some headers and are told to figure it out yourself (many commercial packages like cuda or steam).
The (lack of any) build system is actually nice for flexibility. You can lay out files however you want, link together random object files without extra work, use your own weird dependency tracking, etc. Obviously it's not super easy to get started with compared to Rust et al. but choosing C++ in the first place implies some need for industrial grade features or unusual setup.
Sure, but JS has a myriad of choices too and yet we mostly agree on node_modules, package.json and npm (the repo). Big companies or weirdos are free to swap any of those with something else if they want but the little guys have something standardish if they don't want to inflict too much pain upon themselves.
No. The problem isn’t that std::regex is slow and badly designed. It’s that std::regex exists at all.
C++ is unique in that it defines a spec for STL but not implementation. The result is something that is both overspecified and underspecified.
Including batteries is fine. Including a spec for what the batteries should look like is such a profoundly bad idea that no other major language does it.
I'm confused about what exactly you're arguing for. Is the idea that the standard library should be minimal and then each compiler should ship its own nonstandard "batteries" library?
> By voting “no,” an established system, one based primarily on trust and respectful collaboration, has been shaken.
I don't get it. If ISO deliberately requires two levels of approval, why should exercising the second level's voting authority be considered a betrayal of trust?
A more charitable interpretation is something like royal assent for laws. Yes, the king/queen can always just choose to delay it or even block the law, but that'd be unprecedented and the whole system of parliamentary monarchy would be in a serious crisis.
I think the author is trying to get at like, the actual discussion happens earlier / on the WG21 level, and the ISO vote is treated more of a rubberstamp. And that has changed in this instance.
I don't get it either; and have no sides on the fence (been years since I wrote C++; but I have before).
It sounds like there's sufficiently different genuine views here on whether it's right for the standard at this time, and this seems like the process working as designed.
Correct me if I'm wrong, because I don't follow C++ very closely, but based on previous discussions on HN, the opposition paper obliquely referenced in the blog post was presumably Bjarne Stroustrup's, who IIRC had already said he would work behind the scenes to make sure the final pro forma vote to standardize C++26 would fail.
Bjarne Stroustrup has been pushing Profiles, which would allow C++ code (or the majority of it) to become type-safe and memory safe.
Contracts are useful, but don't guaranteed anything if type safety & memory safety can be bypassed.
I think the ISO panel made the right call. The real world consider memory safety & execution integrity to be critical issues, and C++ no longer to be viable. Without some major improvements -- I would consider this view to be correct.
Yes that's right, and from following some threads on reddit about this, he used some really dirty tactics to get it to fail, like scheduling certain snap elections to happen with very short notice at times of the day when people who would oppose his point of view would likely be asleep.
> ...at times of the day when people who would oppose his point of view would likely be asleep.
Stroustrup is 75 years old. This is not only hard to believe because of his age, but also because it requires that people who oppose his views somehow have distinct sleeping patterns from ones who agree with his views. Weird, man.
> that people who oppose his views somehow have distinct sleeping patterns from ones who agree with his views.
Not weird if they're mostly from different continents.
When I saw him a year or so ago he said he wasn't happy with how things were going, but never alluded to a coup. But it's his language, so good for him.
Reddit is a cesspool, I wouldn't put faith in anything you read there.
There were no "dirty tricks". The C++ standards committee works by a vaguely defined "consensus", which requires more than "the majority rules". Contracts got added to the C++26 draft. Then there was consensus that Contracts needed to be fixed, but they could never get consensus on any particular fix. So they cruised along relatively unchanged.
In the end, the only way to NOT accept a marginal Contracts feature was to vote down the full language spec. Now they'll regroup and decide how to proceed.
> Correct me if I'm wrong, because I don't follow C++ very closely, but based on previous discussions on HN, the opposition paper obliquely referenced in the blog post was presumably Bjarne Stroustrup's (...)
I've noticed that Bjarne Stroustrup is being subjected to a smear campaign, when things are far simpler and far less conspiratorial than they are making out to be.
There are indeed papers demonstrating that not only is the current proposal for contracts broken but it also fails to adhere to core C++ principals. They have been published since at least 2017. Contracts aren't new, nor the problems they introduced. They've been routinely removed from C++ standards, and so far the proposal wasn't fixed.
So ask yourself this: why was a notoriously broken feature forced into the proposal when it was clear it wasn't going to pass?
From an outsider's point of view, I see this from a different perspective. Contracts proponents tried to use bureaucratic tricks and threats of abnormal processes to force a broken feature they knew for years that wasn't supported or passing the smell test. And now that they saw their efforts thwarted , the complain that their plan failed and they have opposition?
I mean, there is even a paper dating back to 2025 called "contracts concerns" and from 2026 called "contracts fundamental flaws". The C++ standard is a consensus-driven process. Does this look like consensus? Clearly no.
So we have a group of people who ignored the calls that they were pushing a broken feature, but tried to railroad the process anyway and ignore any concern or warning. Then, when they tried to force their way through the process, their bluff was called and their threats failed. And now they are lashing back.
An implementation of which exists in the following GitHub repo (albeit implemented in the xvec::simd namespace rather than std::simd...but otherwise intended to be spec-compliant).
Speaking as a long-time C++ developer...I wasn't uninterested in contracts (which I've known about since the days of Bertrand Meyer flogging them in Eiffel), but I agree with the sentiment here that the SIMD efforts were considerably more interesting.
SIMD cannot be solved at the compiler level. The capabilities of silicon SIMD implementations are fundamentally so disjoint that code using SIMD requires contextual and platform-specific data structures and algorithms.
SIMD on different silicon is incompatible at layers of abstraction far above the codegen manipulation a compiler can do.
You'll never get the full feature set of all SIMD implementations in a single generic abstraction but I'm not sure that's the only way a SIMD abstraction could provide value. There is a pretty consistent set of narrow SIMD that behaves close enough to consistently get better performance across generic targets with high level abstractions better than auto vectorized scalar code but worse than platform tuned SIMD.
The subset of SIMD that translates is so narrow that it is almost useless in real code. That’s the problem. Additionally, it is invalid for the compiler to redesign your data structures.
The ability of compilers to use SIMD is no better than it was 20 years ago. Total stagnation for all practical purposes, and the reason is that compilers fundamentally lack the context and freedom to rewrite the code architecture appropriately for SIMD optimization (even if they could).
I think a point people miss is that highly optimized SIMD code is almost never about parallelizing loops. It is about deeply probing and manipulating arbitrarily complex data structures in parallel that involve collections of unrelated types. SIMD allows you to do this, and it is fantastically efficient, but a compiler has no conceivable way of understanding this.
For this reason, SIMD optimization has often been classified as an AI-Complete problem in computer science.
My imagination is failing me, can you give me an example of the type of work being done where SIMD is ‘deeply probing and manipulating arbitrarily complex data structures in parallel that involve collections of unrelated types’? I don’t doubt you know what you mean, but I can’t wrap my head around it.
For me I can only think of the simplest example of SIMD being used to ‘parallelize loops’ as what SIMD is for. If it turns out I’m missing a large problem or application space for SIMD I will be excited to research it. Any pointers to topics would be appreciated.
Is the common feature set described anywhere online? I am not in the SIMD world, and I am curious about the state of it. But I am not so committed that I am wiling to learn several different platforms’ SIMD implementations in order to suss out their commonalities.
There are frameworks trying to unify simd/avx, but the abstractions aren't free. At this point, we need better hardware and low level interfaces, not better abstractions.
If you look at "let's use AI to rewrite xyz in Rust", then C++ has to wonder
why it isn't as often mentioned compared to Rust here. I am not saying AI
should be the future, but merely compare why Rust is cited here more
frequently than C++. That's just one of many other things. Rust also got
popular due to crates. How is the alternative called in C++? Barely anyone
outside the C++ community knows. And that's also a problem.
C++ isn't going away anytime soon, of course, but when people keep on mentioning
alternatives again and again then it shows that the competition intensifed a lot.
If I want to spin up a new project with a coding agent to explore some idea and I'd like the bare metal performance, why would I choose C++ over Rust?
I could choose TypeScript over Rust if I wanted it to be html first or I could choose Go if I wanted it to be clear of the complexity of memory management or I could choose C# if I wanted it to have best interface with windows stuff or I could choose something Erlang VM based for resilience and multithreading.
You'll find plenty of info if you search for anything like "c++ contracts" [0], but the short of it is that they're just pre/post conditions on functions. Slightly improved assertions, basically.
cppreference is often a bit too technical for its own good :)
But I think there's a broader issue which is that if it took me multiple searches to find a good-enough visual "pitch" for what contracts look like in practice, its champions have not yet won hearts and minds - which brings us to the situation at hand.
Its a very inside baseball article. Contracts is a proposed C++ language feature for improving programmable assertions of program state. E.g. a better c++ version of C's assert function. That in theory will improve both safety and performance by letting people add more complex assertions (e.g. pre/post conditions) to functions.
The issue that caused this to be voted down is often seen as a memory safety solution (not something I personally 100% agree with, but thats a broad view). And the rest of this release includes other memory safety work. And it was voted down and delayed for apparent political reasons (again not a view I agree with).
So most people will read your view as hypocritical/misinformed.
It could also be read as a straight up attack. Basically, a way of saying “why not follow Rust“ without having to say the word Rust.
I think it was a fair question. As someone who doesn’t follow C++ I really don’t know what else was in the proposal. It’s nice to hear there is memory safety stuff.
The memory-safety-relevant parts of the proposal could be salvaged without keeping contracts more broadly, by saying that the relevant behaviors (like indexing past the end of a std::vector) cause program termination in hardened builds. I'm sure it's more complicated than this but I don't think much more.
More generally, the C++ committee has had a really hard time agreeing on memory-safety stuff because there are a lot of different constituencies with completely different priorities (especially whether they're using it for greenfield vs. legacy vs. something in between), and the incentive is to make proposals sound good to everyone at the expense of actually being coherent.
you know downvoting without explaining why is part of herd mentality. i expected better on HN. dont you wanna give some reasons as to why you find this offensive?
I feel like this is a bellwether event for society at large. Growing impasses between more and more segments of society. Diminishing trust leading to the inability to reach consensus. Maybe it’s just me though.
Perhaps it is, in this case it would be between money and everyone else specifically. Contracts is a pet project of Microsoft and the heavy money parts of the committee. They've basically shouted down the dissenters, hence the effectively unprecedented action of the rubberstamp portion of the process saying they dont think consensus was reached in a kosher way.
No one who developed contracts works for Microsoft. Of the like 20 people who contributed to the feature, 4 of them work for Bloomberg, so you could maybe argue that Bloomberg has a vested interest in the feature, but that's really stretching things.
Support for contracts is fairly broad and spans numerous organizations.
Even if C++ is irrelevant for new code, there's so much software already written in it that we'll be maintaining it for decades to come. I'd argue that Cobol and Fortran have been mostly obsolete for new code for almost 30 years now, yet both are still widely used today, and they've even had major updates in the past decade [0] [1]. And there's even more software written in C++ than there is in Cobol or Fortran, so I don't think that C++ is going away any time soon.
> Is C++ still relevant? What prevents Rust from completely supplanting it?
A highly mature ecosystem with well-established libraries. Especially in certain fields (DSP, robotics, CAD kernels, microcontrollers, etc.), there are no equivalent libraries and frameworks in Rust with such a proven track record.
Now, LLMs can rewrite those libraries in Rust quite easily. Such options weren't available a few years back. But it's still hard to prove that a rewrite hasn't introduced new bugs. It's easy to demonstrate that a piece of code has bugs, but much harder to prove that it doesn't introduce any new ones.
Essentially all high-end systems code for high-performance and high-reliability systems is still written in modern C++. That language has many attractive properties, including safety features that Rust does not currently support.
Additionally, for pure performance requirements, C++ is still materially faster than Rust in practice. That may change some day. C++ has many issues but it is also objectively excellent at many things.
C++ is the third most popular programming language according to TIOBE behind C and python. It's got an 8.87% ranking. So yes it looks like C++ is still relevant. In fact C++ usage has risen slightly.
Rust is in tenth place with 1.44% ranking, it's rising fast but still has a long way to go before it catches C++.
I'm not going to speculate about why Rust hasn't yet supplanted C++ but I will say I don't find it surprising.
A much more accurate snapshot would be Github - they recently published the top langauges for the year (so far, up til Sept 2026) by distinct monthly contributors and C++ comes in at 9 out of the top 10, and Rust doesn't even place in the top 10 yet, so yes it is highly relevant and prevalent, but not because TIOBE said so.
But, TypeScript, Python and Rust are the fastest growing languages, in that order, so also you cannot discount Rust.
But, of course, there is still a lot of new C++ code written, more than Rust. I believe C++ will become legacy, but it's not there yet and even once that happens it'll take at least decades to stop writing C++.
99.9% of all system code in the world is still written in C/++. It runs your Java, C#, Javascript, Python, PHP, basically every production language that isn't Go or Rust. It runs the two most popular game engines in the world. It runs your phone, server, and laptop, no matter which of any you use. It runs your car. It runs almost every embedded and industrial application on the planet.
Is it still relevant, JFC. The way people on this forum manage to sequester themselves from reality. Let me reverse the question: is Rust relevant? Mozilla developed Rust, abandoned their Rust browser, and only 10% of Firefox is written in Rust. Maybe 1% of modules in Chrome and Linux are written in Rust, if that. And what of Rust applications written from scratch? Can you name ten applications that have, say, exposure to more than 100,000 users? Impossible mode: they can't be developer tools only used by other developers (uv, ripgrep, etc.), they must actually be applications used by enterprises or consumers.
I read that as "is c++ still relevant for new features, given Rust and its popularity", not "who is still using C++".
Personally, I think it is still relevant. Many people thought Kotlin could overtake Java, Java reinvented itself with new initiatives/features and was saved from becoming irrelevant.
Rust also has the LLM advantage which is where I think the "if it compiles it works" nature of Rust is easier for manual changes and maintenance when needed.
Java vs. Kotlin is a different matter. It's still an open question if C++ even could match Rust's features, not to say if it (the committee) wants to, and the answer seems to be "no".
I have no idea why anyone would work in C++ in 2026. If I had to work on an existing codebase, I'd just have Claude rewrite it in Rust. It's always been a miserable, awful mess.
At this point, changes to major programming languages have to adapt to a world in which AI systems generate and change much of the code. C++ contracts may be good or bad, but they are from before strong AI coding systems. So it's time to rethink.
And we have no idea what AI systems will be doing in 2027.
> And we have no idea what AI systems will be doing in 2027.
How would you begin to form a plan of how you'll rethink if you can't even see into next year? Isn't it beneficial not to change the languages too much because there's so much training data for the current revisions? AI does not need to be catered to, that is the whole point and why it is useful.
We're going to need languages which both humans and AIs can read and write.
We don't know what those look like yet. Contracts aren't a bad idea, but C++ has just become too big. Even people who used to be C++ language lawyers have said that.
Not to defend the particular proposal at issue here, but my sense is that contract-like things synergize quite well with AI coding, for the same reasons automated tests and static types do.
A lot of folks, many of them our most capable programmers, are fighting the last war. It’s like they think AI is going away and we’ll all work like it’s 2019 again.
If you were already writing high-reliability C++ then the benefits are difficult to quantify. If you weren’t writing high-reliability C++ then it saves you almost nothing over doing the standard idioms of high-reliability C++ that were already available to you at very marginally more cost. It does standardize expression of it in narrow cases but the payoff seems minimal.
Most of what C++ Contracts delivers is a mashup of what you can already do with constexpr and C++20 Concepts. I like reliability features but this feature, as delivered, looks fairly useless if you already use reliability features. A compelling standard would need to make much deeper guarantees out of the box. And the compiler can already see through most compositions of constexpr and C++20 concepts, which is already very expressive.
C++ Contracts looks a bit like a feature that was designed long before current standard features existed.
One of the best features to be added to C++ in many years.
C++ contracts are an attempt to bring C asserts into the C++ age. The weakness of C++ contracts is that they are mostly syntactic sugar over C asserts. If you really care about this type of thing, you probably already have a custom C++ assertion framework that is at least as capable if not more.
The promise of C++ contracts is that they can aid formal verification, which would be great. As delivered, it can’t do much more than was already possible, which will inhibit adoption.
(IMO the single best improvements over the years have been atomics and maybe variadic templates.)
One thing I give the C++ feature gods credit for is recognizing material deficiencies in systems languages and unapologetically trying to fill those gaps starting with C++11. The addition of atomics, strict variadics, constexpr, lambdas, concepts, lifetime annotations, etc has been transformative for C++.
[0] https://www.youtube.com/watch?v=yhhSW-FSWkE
I think the risk is that C++ contracts become an evolutionary dead-end that hang around forever in code bases because they were standardized. It wouldn’t be the first time this has happened.
Phrased differently, contracts are to concepts what assert is to static_assert.
Contracts notionally offer the ability to lift some runtime assertions to compile-time. That is how it was sold. Except they don’t in practice.
Meanwhile, concepts + constexpr if used artfully deliver that in practice, including for many cases that contracts were supposed to solve.
I push all verification to compile-time to the extent possible.
While the C++26 variant of contracts doesn't provide the benefits of its static-analysis-centric ancestor from 2014, and therefore isn't as consequential a feature, it still provides value to some and is absolutely not important enough to be worth killing a standard. Concepts do not provide this value.
In any case, it's simply false that C++26 contracts are unnecessary because we have concepts, yet this claim is the thrust of your initial comment.
Do you have any information as to why they shifted the focus from static analysis to runtime checks? I only remember that it was based on some Microsoft annotation language or something.
The only extreme and tone deaf thing I see in this story is how contracts proponents were faced with multiple papers demonstrating quite clearly and extensively how they were broken in specification and in form, but still tried to ignore all the criticism and force them through a consensus process in spite of being clearly opposed.
How does this make any sense? What was the plan here? To blackmail the C++ community to accept a broken feature under threat of the proposal not passing?
Make it make sense?
What I want to see is the people who tried to force contacts upon the process in spite of all opposition to come forth and explain their rationale. It was highly absurd and even unthinkable to force a broken feature down C++'s throats with bureaucratic chicanery, and then complain that the same bureaucracy has mechanisms to stop it's abuse. I for one would like to hear an explanation.
I put together an alternative function contract and invariant mechanism in C using CBMC and custom macros that effectively allows me to perform formal methods in C using compositional verification. The reason why I chose C is because of its relative simplicity and relative ease of building tooling around it. C++ contracts provide some feature parity, and would let me take advantage of some of the features in C++ relative to C.
I hope that the contract proposal is workshopped and simplified so it can be proposed again for a future version. Its current form is unsuitable, but it deserves a second chance with a simpler implementation. Contracts would narrow the safety gap between C++ and languages such as Ada / SPARK.
I think the ISO panel made the right call. The real world consider memory safety & execution integrity to already be critical issues (and C++ no longer to be viable), and they are correct. The WG has its priorities wrong.
Like for example, Coroutines were billed as an easier way to write concurrent code, but personally I think it completely failed and ended up being hopelessly complex and confusing. Modules are the same - superficially they make things simpler, but when people actually go to adopt it, the details are so complex that nobody bothers.
Like most people in this thread, you should really read up on contracts before commenting. The contracts proposal is for runtime assertions, and their problem is that they are poorly specified and fundamentally broken. Their proponents haven't been addressing any of their concerns and tried to push a half baked version of them down everyone's throats, which was why they failed to pass.
Spoiler alert: The option described as "the sort of leadership failing that I pray we can avoid" is what ended up happening.
I mean, I mainly say this to joke because it's probably unfixable at this point, but whenever I mess with it, I'm struck by how hard/opaque C++ makes this problem compared to most other languages.
Large FAANGs that would be incentivized to change it don't care because they have their own in-house C++ build systems like bazel (Google) or buck2 (Meta) that are far faster than cmake (distributed compilation and caching) but require huge teams to maintain. Unfortunately, this distributed compilation and caching layer is something that many other languages don't have since their build systems are made for single devs building locally.
Also the dependencies can be added in a myriad of ways. Your build system can download them, your meta-build dependency manager can find them (Conan), your Linux distro can provide them (system libraries), or maybe you just download an object file from a website + some headers and are told to figure it out yourself (many commercial packages like cuda or steam).
C++ is unique in that it defines a spec for STL but not implementation. The result is something that is both overspecified and underspecified.
Including batteries is fine. Including a spec for what the batteries should look like is such a profoundly bad idea that no other major language does it.
The ISO National Bodies voted wisely. C++ has had so many ill defined features over the decades and they wanted to avoid yet another one.
I don't have any skin in the game. I've stayed with the C++11 feature set.
I don't get it. If ISO deliberately requires two levels of approval, why should exercising the second level's voting authority be considered a betrayal of trust?
That’s not very charitable, but honestly I’ve been trying for five minutes now to find or think up an alternative explanation. And coming up blank.
I think the author is trying to get at like, the actual discussion happens earlier / on the WG21 level, and the ISO vote is treated more of a rubberstamp. And that has changed in this instance.
That's my opinion as well. It's a smear campaign lashing back at people who dared to point out flaws.
It sounds like there's sufficiently different genuine views here on whether it's right for the standard at this time, and this seems like the process working as designed.
Contracts are useful, but don't guaranteed anything if type safety & memory safety can be bypassed.
I think the ISO panel made the right call. The real world consider memory safety & execution integrity to be critical issues, and C++ no longer to be viable. Without some major improvements -- I would consider this view to be correct.
Stroustrup is 75 years old. This is not only hard to believe because of his age, but also because it requires that people who oppose his views somehow have distinct sleeping patterns from ones who agree with his views. Weird, man.
Not weird if they're mostly from different continents.
When I saw him a year or so ago he said he wasn't happy with how things were going, but never alluded to a coup. But it's his language, so good for him.
There were no "dirty tricks". The C++ standards committee works by a vaguely defined "consensus", which requires more than "the majority rules". Contracts got added to the C++26 draft. Then there was consensus that Contracts needed to be fixed, but they could never get consensus on any particular fix. So they cruised along relatively unchanged.
In the end, the only way to NOT accept a marginal Contracts feature was to vote down the full language spec. Now they'll regroup and decide how to proceed.
I've noticed that Bjarne Stroustrup is being subjected to a smear campaign, when things are far simpler and far less conspiratorial than they are making out to be.
There are indeed papers demonstrating that not only is the current proposal for contracts broken but it also fails to adhere to core C++ principals. They have been published since at least 2017. Contracts aren't new, nor the problems they introduced. They've been routinely removed from C++ standards, and so far the proposal wasn't fixed.
So ask yourself this: why was a notoriously broken feature forced into the proposal when it was clear it wasn't going to pass?
From an outsider's point of view, I see this from a different perspective. Contracts proponents tried to use bureaucratic tricks and threats of abnormal processes to force a broken feature they knew for years that wasn't supported or passing the smell test. And now that they saw their efforts thwarted , the complain that their plan failed and they have opposition?
I mean, there is even a paper dating back to 2025 called "contracts concerns" and from 2026 called "contracts fundamental flaws". The C++ standard is a consensus-driven process. Does this look like consensus? Clearly no.
So we have a group of people who ignored the calls that they were pushing a broken feature, but tried to railroad the process anyway and ignore any concern or warning. Then, when they tried to force their way through the process, their bluff was called and their threats failed. And now they are lashing back.
https://en.cppreference.com/cpp/experimental/simd
An implementation of which exists in the following GitHub repo (albeit implemented in the xvec::simd namespace rather than std::simd...but otherwise intended to be spec-compliant).
https://github.com/intel/xvec
Speaking as a long-time C++ developer...I wasn't uninterested in contracts (which I've known about since the days of Bertrand Meyer flogging them in Eiffel), but I agree with the sentiment here that the SIMD efforts were considerably more interesting.
SIMD on different silicon is incompatible at layers of abstraction far above the codegen manipulation a compiler can do.
The ability of compilers to use SIMD is no better than it was 20 years ago. Total stagnation for all practical purposes, and the reason is that compilers fundamentally lack the context and freedom to rewrite the code architecture appropriately for SIMD optimization (even if they could).
I think a point people miss is that highly optimized SIMD code is almost never about parallelizing loops. It is about deeply probing and manipulating arbitrarily complex data structures in parallel that involve collections of unrelated types. SIMD allows you to do this, and it is fantastically efficient, but a compiler has no conceivable way of understanding this.
For this reason, SIMD optimization has often been classified as an AI-Complete problem in computer science.
For me I can only think of the simplest example of SIMD being used to ‘parallelize loops’ as what SIMD is for. If it turns out I’m missing a large problem or application space for SIMD I will be excited to research it. Any pointers to topics would be appreciated.
If you look at "let's use AI to rewrite xyz in Rust", then C++ has to wonder why it isn't as often mentioned compared to Rust here. I am not saying AI should be the future, but merely compare why Rust is cited here more frequently than C++. That's just one of many other things. Rust also got popular due to crates. How is the alternative called in C++? Barely anyone outside the C++ community knows. And that's also a problem.
C++ isn't going away anytime soon, of course, but when people keep on mentioning alternatives again and again then it shows that the competition intensifed a lot.
what is it though? vcpkgs/decentralized repositories?
If I want to spin up a new project with a coding agent to explore some idea and I'd like the bare metal performance, why would I choose C++ over Rust?
I could choose TypeScript over Rust if I wanted it to be html first or I could choose Go if I wanted it to be clear of the complexity of memory management or I could choose C# if I wanted it to have best interface with windows stuff or I could choose something Erlang VM based for resilience and multithreading.
But what reason might I have to pick C++?
But they say this is the first case where a DIS failed during the standardization consensus process. Why is that?
[0] https://en.cppreference.com/cpp/language/contracts
cppreference is often a bit too technical for its own good :)
But I think there's a broader issue which is that if it took me multiple searches to find a good-enough visual "pitch" for what contracts look like in practice, its champions have not yet won hearts and minds - which brings us to the situation at hand.
EDIT: Would love to know why people are so angry about that?
So most people will read your view as hypocritical/misinformed.
I think it was a fair question. As someone who doesn’t follow C++ I really don’t know what else was in the proposal. It’s nice to hear there is memory safety stuff.
More generally, the C++ committee has had a really hard time agreeing on memory-safety stuff because there are a lot of different constituencies with completely different priorities (especially whether they're using it for greenfield vs. legacy vs. something in between), and the incentive is to make proposals sound good to everyone at the expense of actually being coherent.
- let us say tomorrow everyone were to consider removing all unsigned variables across c++
- what is the impact in terms of compatibility for all the old c++ applications which i believe would be millions of them if not billions?
- the reason i ask is they say do not unsigned anything as much as you can because overflowing the bottom below 0 is easy
- has there ever been any consideration to get rid of unsigned xyz in c++?
Support for contracts is fairly broad and spans numerous organizations.
I pretty much do all my low level vibe coding in Rust. Is C++ still relevant? What prevents Rust from completely supplanting it?
[0]: https://en.wikipedia.org/wiki/COBOL#COBOL_2023
[1]: https://en.wikipedia.org/wiki/Fortran#Fortran_2023
A highly mature ecosystem with well-established libraries. Especially in certain fields (DSP, robotics, CAD kernels, microcontrollers, etc.), there are no equivalent libraries and frameworks in Rust with such a proven track record.
Now, LLMs can rewrite those libraries in Rust quite easily. Such options weren't available a few years back. But it's still hard to prove that a rewrite hasn't introduced new bugs. It's easy to demonstrate that a piece of code has bugs, but much harder to prove that it doesn't introduce any new ones.
Additionally, for pure performance requirements, C++ is still materially faster than Rust in practice. That may change some day. C++ has many issues but it is also objectively excellent at many things.
Rust is in tenth place with 1.44% ranking, it's rising fast but still has a long way to go before it catches C++.
I'm not going to speculate about why Rust hasn't yet supplanted C++ but I will say I don't find it surprising.
A much more accurate snapshot would be Github - they recently published the top langauges for the year (so far, up til Sept 2026) by distinct monthly contributors and C++ comes in at 9 out of the top 10, and Rust doesn't even place in the top 10 yet, so yes it is highly relevant and prevalent, but not because TIOBE said so.
But, TypeScript, Python and Rust are the fastest growing languages, in that order, so also you cannot discount Rust.
https://github.blog/news-insights/octoverse/octoverse-commit...
But, of course, there is still a lot of new C++ code written, more than Rust. I believe C++ will become legacy, but it's not there yet and even once that happens it'll take at least decades to stop writing C++.
Is it still relevant, JFC. The way people on this forum manage to sequester themselves from reality. Let me reverse the question: is Rust relevant? Mozilla developed Rust, abandoned their Rust browser, and only 10% of Firefox is written in Rust. Maybe 1% of modules in Chrome and Linux are written in Rust, if that. And what of Rust applications written from scratch? Can you name ten applications that have, say, exposure to more than 100,000 users? Impossible mode: they can't be developer tools only used by other developers (uv, ripgrep, etc.), they must actually be applications used by enterprises or consumers.
Personally, I think it is still relevant. Many people thought Kotlin could overtake Java, Java reinvented itself with new initiatives/features and was saved from becoming irrelevant.
Rust also has the LLM advantage which is where I think the "if it compiles it works" nature of Rust is easier for manual changes and maintenance when needed.
Even in their case. Rust depends on LLVM which is wriiten in C++. Go needs libc on some platforms.
And we have no idea what AI systems will be doing in 2027.
>
> And we have no idea what AI systems will be doing in 2027.
How would you begin to form a plan of how you'll rethink if you can't even see into next year? Isn't it beneficial not to change the languages too much because there's so much training data for the current revisions? AI does not need to be catered to, that is the whole point and why it is useful.