testing for proximity to end of iterator in all cases except input iterator.

main.cpp

#include <string>
#include <iostream>
#include <vector>
#include <array>
#include <set>
#include <unordered_set>

template<typename T>
void printElems(T elems) {
    std::cout << "[ ";
    for (auto itr = elems.begin(); itr != elems.end(); ++itr) {
        std::cout << *itr;
        
        // test proximity
        auto next = itr;
        ++next;
        if (next != elems.end()) std::cout << ", ";
    }
    std::cout << " ]\n";
}

int main() {
    std::vector<uint64_t> vec{1, 2, 3, 4, 5, 6};
    printElems(vec);
    
    std::array<uint64_t, 5> ary{1, 2, 3, 4, 5};
    printElems(ary);
    
    std::set<uint64_t> set{1, 2, 3, 4};
    printElems(set);
    
    std::set<uint64_t> uset{1, 2, 3, 4};
    printElems(uset);
    
    return 0;
}

Output:

[ 1, 2, 3, 4, 5, 6 ]

[ 1, 2, 3, 4, 5 ]

[ 1, 2, 3, 4 ]

[ 1, 2, 3, 4 ]