auto i = {5}; is a std::initializer_list<int>, whereas auto i{5}; is an int (as of C++17): https://godbolt.org/g/eXXN3o https://godbolt.org/g/eXXN3o See

auto i = {5}; is a std::initializer_list<int>, whereas auto i{5}; is an int (as of C++17): https://godbolt.org/g/eXXN3o https://godbolt.org/g/eXXN3o See also https://stackoverflow.com/questions/25612262/why-does-auto-x3-deduce-an-initializer-list https://stackoverflow.com/questions/25612262/why-does-auto-x... .