https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78830
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |INVALID
Target Milestone|--- |10.0
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I don't think it's conforming to reject this at compile-time, because
std::prev(it, -1) is equivalent to std::advance(it, 1) which is valid for
forward iterators. So libc++ has a bug, it is not allowed to reject forward
iterators unconditionally (only when it can prove the argument to prev is
greater than zero).
The best we can do is check for negative values at runtime and abort, which we
already do.
One day I hope to be able to enhance those assertions to warn at compile-time
if the compiler can tell the assertion will fail, but that is not currently
possible.
