Parsing map

map.cpp

using StringMap = std::map<std::string, std::string>;

// From null: [json.exception.type_error.302] type must be object, but is null
try { StringMap m = json(); }
catch (std::exception& e) { std::cout << "From null: " << e.what() << std::endl; }

// From non-object: [json.exception.type_error.302] type must be object, but is number
try { StringMap m = json(42); }
catch (std::exception& e) { std::cout << "From number: " << e.what() << std::endl; }

// From non-string: [json.exception.type_error.302] type must be string, but is number
try { StringMap m = json({ { "a", 42 } }); }
catch (std::exception& e) { std::cout << "From non-string: " << e.what() << std::endl; }

// Works.
{
    StringMap m = json({ { "a", "x" }, { "b", "y" }, { "c", "z" } });
    for (const auto& p : m)
    {
        std::cout << p.first << " -> " << p.second << std::endl;
    }
}