The problem is that for function templates, member functions of class templates, and inline functions, the semantic is essentially assigned randomly if it is used in multiple TUs that are compiled with different semantics. 

In most complex environments you are dealing with things like libraries that are provided by others, so you may not have control over how it is built.

You can also have two libraries that use a third library, but if those two libraries are a different semantic any user of the third library has no idea what semantic they’ll get even if their code also uses the third library and is built with a particular semantic.

John.

On Oct 17, 2025, at 11:45 AM, Gašper Ažman via SG21 <sg21@lists.isocpp.org> wrote:

+1 to what Tom said.

One part of this discussion is speaking as if semantics are assigned randomly or arbitrarily, where they are assigned by the person who ships the product - it has been pointed out time and time again that the actor deploying the application is the final arbiter of what "safe" means for a given contract check, because it's actually a function of "safe(context) -> bloom" (where "bloom" is a type with exactly two values of "no" and "perhaps").

The stakeholder with the best context is the deployer of the application; the farther away you go from that stakeholder, the less context they have. Deferring the choice of semantic to as late as possible gives a better outcome.

On Fri, Oct 17, 2025 at 4:33 PM Tom Honermann via SG21 <sg21@lists.isocpp.org> wrote:

On Oct 17, 2025, at 10:23 AM, Harald Achitz via SG21 <sg21@lists.isocpp.org> wrote:


On 2025-10-17 16:00, René Ferdinand Rivera Morell wrote:
On Fri, Oct 17, 2025 at 8:53 AM Harald Achitz via SG15 <sg15@lists.isocpp.org> wrote:

Today's

void fun(Foo* ptr)  {
my_supper_assert_macro (ptr!=nullpter);
my_supper_assert_macro(ptr->hasData());
 }

should not have any problems, ever


AFAIU, if my_supper_assert_macro implements something equivalent to observe, that is still UB at present. Or is it EB now?

--
-- René Ferdinand Rivera Morell
-- Don't Assume Anything  -- No Supongas Nada
-- Robot Dreams - http://robot-dreams.net


On devices that keep you alive, one example where I have seen such super asserts in action, contracts are contracts They do not exist only sometimes. 

Correct, (plain language) contracts are omnipresent. The contract checking statements above violate the function contract and are thus defective. Static analysis can diagnose such cases. For example, I would expect a contracts enabled version of Coverity to report a FORWARD_NULL issue for the above code. 


I am not even sure if contracts as specified would pass regulatory requirements, I think not. 

I’m not an expert on the subject by any means, but I would expect regulatory requirements to consider the manner in which the software is built; just as they consider the content of the source code and require other supply chain guards. A requirement that deployed software not contain portions for which the observe semantic is selected seems reasonable and prudent.

Tom. 

/Harald

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