https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117849
--- Comment #5 from Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> --- Thanks for looking into this issue! Yes, GCC is currently the compiler that comes closest to implementing P2280 - Clang fails on so many more examples here. However, WG21 just voted library wording into the working draft that relies on this feature. :-) I modified your reduced example to be closer to the original code. (ranges::size(r) returns r.size(); integral_constant (i) is convertible to the value, making it comparable - no need for operator==). I also added a 'size(t) > 0' check and a check for a type that is not statically sized, where the concept shouldn't become ill-formed either. https://godbolt.org/z/dE6sjnaKP ``` template <int N> struct a { constexpr int size () const { return N; } }; struct v { int _size = 3; constexpr int size () const { return _size; } }; template <int N> struct i { constexpr operator int () const { return N; } }; template <typename T> constexpr auto size (T &&t) { return t.size (); } template <typename T> concept StaticSizedRange = requires (T &&t) { typename i<size(t)>; requires (size (t) > 0); }; a<5> b; static_assert (size (b) == size (b)); static_assert (StaticSizedRange<a<5>>); static_assert (StaticSizedRange<a<5> &>); static_assert (StaticSizedRange<const a<5> &>); // a std::vector is not a statically sized range static_assert (!StaticSizedRange<v>); ```
