On Tue, 25 Apr 2023 at 14:39, Thiago Macieira via Std-Discussion <std-discussion@lists.isocpp.org> wrote:

On Tuesday, 25 April 2023 11:53:46 PDT Lukas Barth via Std-Discussion wrote:
> At this point I'm at my wit's end. How is that rule to be interpreted?

Why are you trying to interpret it? Can't you just assume that if the type
isn't a trivial scalar, it can't be passed?

An enum is a trivial scalar.

> Could it be that this use of "compatible" in `[stdarg.syn]/1.2` was

grandfathered in from C, but is not defined anymore?

Yes.

> What is "the type that results when passing an argument for which

there is no parameter"?

See http://eel.is/c++draft/expr.call#11.sentence-1 . In other words, you can use a parameter as the second argument to va_start if it is a type such that you could retrieve it from ellipsis using va_arg (i.e., if there was a preceding parameter).