https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98639
--- Comment #5 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> --- Meh, I guess this is just an unintended (but conforming) consequence of the shifting C++17/20 rules. Jonathan links to https://twitter.com/wakomeup/status/1274778577087627267 as another example: // https://godbolt.org/z/WWr9b8 Base b; const Derived& rd = b; // ill-formed forever, I hope const Derived& rd{b}; // ill-formed until '14, OK in '17 and later const Derived& rd(b); // ill-formed until '17, OK in '20 and later It remains _surprising_ that you can make a `Derived` out of a `Base` in the absence of a constructor... but that's just the new aggregate-paren-init rules at work. It remains _surprising_ that you can bind a `const Derived&` to a `Base&` without a cast... but that's just the interaction of lifetime extension with the new aggregate-init rules. I do think it'd be nice for GCC to give some sort of diagnostic here. But I guess it would have to be an opt-in diagnostic switch. And we already have that switch today; it's called `-std=c++17`. ;) So maybe there's really no way to improve the situation here at all, and this can be closed as NOTABUG.
