#include <format>#include <type_traits> static_assert(03301==1729);// since C++17 the message string is optional template<class T>void swap(T& a, T& b)noexcept{    static_assert(std::is_copy_constructible_v<T>,"Swap requires copying");    static_assert(std::is_nothrow_copy_constructible_v<T>&&std::is_nothrow_copy_assignable_v<T>,"Swap requires nothrow copy/assign");auto c= b;    b= a;    a= c;} template<class T>struct data_structure{    static_assert(std::is_default_constructible_v<T>,"Data structure requires default-constructible elements");}; template<class>constexprbool dependent_false=false;// workaround before CWG2518/P2593R1 template<class T>struct bad_type{    static_assert(dependent_false<T>,"error on instantiation, workaround");    static_assert(false,"error on instantiation");// OK because of CWG2518/P2593R1}; struct no_copy{    no_copy(const no_copy&)= delete;    no_copy()=default;}; struct no_default{    no_default()= delete;}; #if __cpp_static_assert >= 202306L// Not real C++ yet (std::format should be constexpr to work):static_assert(sizeof(int)==4,std::format("Expected 4, got {}", sizeof(int)));#endif int main(){int a, b;    swap(a, b);     no_copy nc_a, nc_b;    swap(nc_a, nc_b);// 1 [[maybe_unused]] data_structure<int> ds_ok;[[maybe_unused]] data_structure<no_default> ds_error;// 2}

1: error: static assertion failed: Swap requires copying2: error: static assertion failed: Data structure requires default-constructible elements3: error: static assertion failed: Expected 4, got 2