On Thu, 17 Jun 2021, 19:19 Jonathan Wakely, <jwakely....@gmail.com> wrote:
> > > On Thu, 17 Jun 2021, 16:50 Patrick Palka via Libstdc++, < > libstd...@gcc.gnu.org> wrote: > >> This implements the wording changes of P2325R3 "Views should not be >> required to be default constructible". Changes are relatively >> straightforward, besides perhaps those to __box (which now stands >> for copyable-box instead of semiregular-box) and __non_propagating_cache. >> >> For __box, this patch implements the recommended practice to also avoid >> std::optional when the boxed type is nothrow_move/copy_constructible. >> >> For __non_propagating_cache, now that it's used by split_view::_M_current, >> we need to add assignment from a value of the underlying type to the >> subset of the std::optional API implemented for the cache (needed by >> split_view::begin()). Hence the new __non_propagating_cache::operator= >> overload. >> >> While we're changing __box, this fixes the undesirable list-init in >> the constuctors of the partial specialization as reported in PR100475 >> comment #7. > > > > As I said on IRC, I'm not sure why the defaulted default constructors need > to be constrained (rather than just letting them get deleted) but the patch > is OK. > Because the default member initializers are in the immediate context, so the constructor would look valid to is_default_constructible, and only get deleted when instantiated. (Thanks to Barry for reminding me of that.) >
