https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113853
Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> changed:
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--- Comment #1 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> ---
(Sorry, not sure where's the best place to put this comment. Maybe nowhere. ;))
You probably know this already, but just in case anyone's not on the same page
yet:
https://eel.is/c++draft/except.throw#5
> When the thrown object is a class object, the constructor selected for the
> copy-initialization *as well as the constructor selected for a
> copy-initialization considering the thrown object as an lvalue* shall be
> non-deleted and accessible, even if the copy/move operation is elided.
That paragraph is lurking in the background every time we talk about GCC's
handling of move-only exception objects. However, my impression is that the
paragraph is ignorable from the vendor's point of view:
- Even on paper, this "shall" is talking only about the runtime behavior "when
an exception _is_ thrown," so it doesn't change anything about the
well-formedness of _unevaluated_ throw-expressions.
- GCC+Clang _probably could_ conformingly decide that it should be ill-formed
to `throw x` when `x` is move-only; but that would break a lot of users, so
pragmatically they can't do that. GCC+Clang need a consistent theory of what it
means to throw a move-only type, and the theory can't possibly be "it's
ill-formed" (because that would break users), so the theory must agree with
Marek's test case: `throw t` ought to be well-formed in C++20-and-later (by
wording introduced to C++20 in P1155 a.k.a. P1825).
IOW, this bug and test case are *not* invalidated by [except.throw]/5. That's
all. :)
