On Tue, 14 Oct 2025 at 13:21, John Spicer via SG15
<sg15_at_[hidden]> wrote:
>
> You say "even if P2900 does not fix linking issues that are not inherent to Contracts”, but the point of P3835 is that the issues *are* inherent to contracts.
>
> The reason for this is that if you currently use a macro like MY_LIB_ASSERT(x), then you have control over what it does, even when your header is used by someone else. If you fail to get this right, it is an ODR violation. So you have done something that makes your program ill-formed, and your tools might be able to detect this.
>
> But if you use contracts, it is not an ODR violation, even when the functions end up doing different things.

Right. P3846 says "This approach enables the use of ODR checkers". But
it doesn't. It disables such checkers. Implementations
can't reject mixed mode builds, even if they think there's some
combination of chosen semantics that's undesirable.

> So, contracts introduce a new problem that other mechanisms, including C assert, do not have.

..and, while claiming to solve ODR-related problems, the result is
that all the practical problematic consequences of
such ODR-related problems remain, but certain implementation
techniques that work for solving them are now not allowed.

In its description of various implementation strategies for mixed-mode
builds, P2900 says
"All these options are, of course, vastly better than making any
program with mixed configurations
IFNDR. "

I do not know where that "of course" comes from, because that claim
doesn't seem to be entirely correct.