How to iterate over a JSON in JSON for modern c++

The nlohmann json library promotes itself as "JSON for modern C++" and aspires to behave "just like an STL container". There is, however, no container in the C++ standard library that is both "vector-like" and "map-like", and that supports both begin/end iterators over values, and begin/end iterators over key/value pairs. So something new is needed.

nlohmann's original solution was to copy jsoncpp's approach, which supports begin/end iterators for json arrays, and adds a distinctly unstandard key() function to the iterator to also support json objects. So you could write

for (auto it = RecentFiles.begin(); it != RecentFiles.end(); ++it){    std::cout << it.key() << "\n";    std::cout << (*it)["Name"].get<std::string>() << "\n";    std::cout << (*it)["Last modified"].get<std::string>() << "\n";}

But being an unstandard way of iterating over key/values, this doesn't have standard library support for range based for loops over key/values.

nlohmann later added the json::items() function that does support iteration over json objects with standard iterators, and which does have standard library support for range based for loops, viz.

int main(){    json RecentFiles;    RecentFiles["1"]["Name"] = "test1.txt";    RecentFiles["1"]["Last modified"] = "monday";    RecentFiles["1"]["Score"] = 5.0f;    RecentFiles["2"]["Name"] = "test2.txt";    RecentFiles["2"]["Last modified"] = "tuesday";    RecentFiles["2"]["Score"] = 5.0f;    for (const auto& item : RecentFiles.items())    {        std::cout << item.key() << "\n";        for (const auto& val : item.value().items())        {            std::cout << "  " << val.key() << ": " << val.value() << "\n";        }    }    std::cout << "\nor\n\n";    for (const auto& item : RecentFiles.items())    {        std::cout << item.key() << "\n";        std::cout << "  " << item.value()["Name"].get<std::string>() << "\n";        std::cout << "  " << item.value()["Last modified"].get<std::string>() << "\n";        std::cout << "  " << item.value()["Score"].get<double>() << "\n";    }}

Output:

1  Last modified: "monday"  Name: "test1.txt"  Score: 5.02  Last modified: "tuesday"  Name: "test2.txt"  Score: 5.0or1  test1.txt  monday  52  test2.txt  tuesday  5