You keep saying things like we have “decades of experience with macro-based systems”.

If contracts were remotely similar to macro-based systems, we would not be having this discussion.

The problem is that contracts are *vastly* different.

If you put P2900 and macro-based systems in the same set, that means you don’t understand one or the other.

John.

> On Oct 20, 2025, at 2:22 PM, Ryan McDougall via SG21 <sg21_at_[hidden]> wrote:
>
> The "course corrections" do not actually suggest a future course (beyond asserting without evidence"we need more experience" and kicking the can down the road to a TS) -- we've had years for alternative proposals to be put forward, and none have surpassed P2900.
>
> We *do* have decades of experience with macro-based systems, we *do* have decades of experience building software at scale (see Software Engineering at Google <https://abseil.io/resources/swe-book>), and we *do* know who our users are (see P1995 and P3297) -- and while there are many variations on contracts, P2900 represents our best consensus interpretation of those decades of experience. Not all of these decisions were everyone's first choice, but P2900 is the consensus. There is no evidence that any other option would improve that.
>
> Multiple papers, like P2900 and P3578 <http://wg21.link/p3578> explain exactly who the feature is for, and how and why each of these design choices were made. There is no reason to believe the current course is incorrect, or that another course would be more correct.
>
> On Mon, Oct 20, 2025 at 4:58 AM Ville Voutilainen via SG21 <sg21_at_[hidden] <mailto:sg21_at_[hidden]>> wrote:
>> On Mon, 20 Oct 2025 at 14:34, Timur Doumler via SG15
>> <sg15_at_[hidden] <mailto:sg15_at_[hidden]>> wrote:
>> > Given the above, it seems to me like opposing C++26 contract assertions because you want that checks are always on / always enforced is kinda like this:
>> >
>> > – Alice: "I want safer roads for pedestrians." (reasonable and good request)
>> > – Bob: "Here's a proposal to fund bike lanes in the city." (reasonable and good proposal roughly in the same area but with a different goal)
>> > – Alice: "But bike lanes don't add more crosswalks or reduce speed limits. So they don't make roads safer for pedestrians. Therefore, we should not build bike lanes."
>> >
>> > Here, Alice is committing a logical fallacy. Just because bike lanes are not useful for Alice, it doesn't mean that they're not useful for Bob, and taking away bike lanes from Bob does nothing to give Alice what she wants.
>>
>> The colorful analogy doesn't include considerations where providing
>> bike lanes for Bob and doing nothing else is not entirely harmless for
>> the pedestrians Alice is focused on.
>>
>> It's also incorrect in its suggestion that bike lanes are not useful
>> for Alice. Nobody has said that P2900 isn't useful. That's why it's
>> included
>> in *every* *single* *one* of the currently active proposals suggesting
>> course corrections.
>> _______________________________________________
>> SG21 mailing list
>> SG21_at_[hidden] <mailto:SG21_at_[hidden]>
>> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/sg21
>> Link to this post: http://lists.isocpp.org/sg21/2025/10/11436.php
> _______________________________________________
> SG21 mailing list
> SG21_at_[hidden]
> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/sg21
> Link to this post: http://lists.isocpp.org/sg21/2025/10/11499.php