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#include <iterator>
#include <vector>
#include <stdexcept>
 
template <typename It>
typename std::iterator_traits<It>::reference
access(It it, It end) {
    return it == end? throw std::runtime_error("no element"): *it;
}
 
int main()
{
    std::vector<int> v;
    access(v.begin(), v.end());
}

prog.cpp: In instantiation of ‘typename std::iterator_traits<_Iterator>::reference access(It, It) [with It = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; typename std::iterator_traits<_Iterator>::reference = int&]’:
prog.cpp:14:30:   required from here
prog.cpp:8:64: error: invalid initialization of non-const reference of type ‘std::__iterator_traits<__gnu_cxx::__normal_iterator<int*, std::vector<int> >, true>::reference {aka int&}’ from an rvalue of type ‘int’
     return it == end? throw std::runtime_error("no element"): *it;
                                                                ^
prog.cpp: In function ‘typename std::iterator_traits<_Iterator>::reference access(It, It) [with It = __gnu_cxx::__normal_iterator<int*, std::vector<int> >; typename std::iterator_traits<_Iterator>::reference = int&]’:
prog.cpp:9:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

Standard output is empty