1 2 template<typename _Callable> 3 struct Base 4 { BaseBase5 Base (const _Callable &) 6 requires true 7 {} 8 }; 9 10 template<typename _Callable> 11 struct Derived : Base<_Callable> 12 { 13 using Base<_Callable>::Base; 14 }; 15 16 template<typename _Callable> 17 Derived (_Callable) -> Derived<_Callable>; 18 19 inline Derived all = [] (auto&& __r) {}; 20