On Mon, Jan 13, 2025 at 5:05 PM mauro russo via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> In the actual standard draft,
>
> §11.7.3 [class.virtual] - p2, p6
>
> read something that seems to be contradiction:
>
> p2 text:
> If a virtual member function F is declared in a class B, and, in a class D
> derived (directly or indirectly) from B, a declaration of a member function
> G corresponds (6.4.1) to a declaration of F , ignoring trailing
> requires-clauses, then G overrides F. ...
>
> p6 text:
> A virtual function shall not have a trailing requires-clause.
>
> It seems the text of p2 allows the presence of trailing requires-clauses
> in virtual functions, both in the original and the overriding declarations
> (note the plural in p2 text), whereas p6 text states the opposite.
>

You don't know whether the derived class function is virtual until you
check whether it overrides a virtual function from the base class. So you
have to ignore the trailing requires-clause on the derived class function
in order to check whether it overrides, and if it does, then the trailing
requires-clause is ill-formed.


>
> However, it's clear that constraints would not be manageable for virtual
> functions. Indeed, the comment during the example in p6 also reads more
> specifically that "virtual function cannot be constrained ".
>
> Now, one might think that the part of p2 "ignoring trailing
> requires-clauses" does not necessarily mean that they can be present, and
> it might be read, instead, as a kind of confirmation that they cannot.
> However, why specifying such a detail only for trailing requires-clauses,
> not even for type-constraints, and requires-clauses ? I mean, even these
> other forms of constraints cannot be present, from
> §13.7.3 [temp.mem] - p3 and p4,
> p3: "A member function template shall not be declared virtual."
> p4: "A specialization of a member function template does not override a
> virtual function from a base class."
>
>
> I guess that, for consistency, the part "ignoring trailing
> requires-clauses" should be removed.
>
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-- 
*Brian Bi*