On Sun, 16 Apr 2023 at 19:35, Andrey Semashev via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> On 4/17/23 01:28, Edward Catmur wrote:
> >
> > On Sun, 16 Apr 2023 at 19:26, Andrey Semashev via Std-Discussion
> > <std-discussion_at_[hidden]
> > <mailto:std-discussion_at_[hidden]>> wrote:
> >
> > On 4/17/23 00:57, Edward Catmur wrote:
> > >
> > > On Sun, 16 Apr 2023 at 18:29, Andrey Semashev via Std-Discussion
> > > <std-discussion_at_[hidden]
> > <mailto:std-discussion_at_[hidden]>
> > > <mailto:std-discussion_at_[hidden]
> > <mailto:std-discussion_at_[hidden]>>> wrote:
> > >
> > > On 4/16/23 22:30, Edward Catmur wrote:
> > > >
> > > > Those are both scope_exit, though, not scope_success or
> > scope_failure.
> > > > When would it make sense to return one of the latter two or
> > to use
> > > them
> > > > at namespace scope?
> > >
> > > If you define it so that scope_fail is called when main() or a
> > thread
> > > entry function is left with an exception, it could be used for
> > the final
> > > cleanup before program termination. For example, collect a
> > backtrace
> > > before terminating or emit a critical message in the log.
> > >
> > > I think uncaught_exceptions() can only be 0 or 1 at that point,
> > though,
> > > so you may as well test it directly and not have to worry about the
> > > cached value being nonzero?
> >
> > Yes, you could. But scope_fail does that for you, so why would you?
> >
> > You might worry that the initializer could be (refactored and)
> > accidentally invoked from a dynamic scope where uncaught_exceptions() is
> > nonzero.
>
> I'm not sure I understand. How a namespace-scope scope guard could be
> initialized while an exception is in flight? Do you mean some weird case
> with shared library loading?
>

More that it could be refactored to a block-scope static. Think about
iostream; it's not inconceivable that the first time std::ios_base::Init is
constructed is while an exception is in flight.