string_view as a key in ordered_json

[fa66ot]

Hello, is the string_view permitted as a key in ordered_json?
Build fails on the below code (the same works Ok for the 'normal' json):

#include "json.h"
#include <string_view>

using namespace std;
using json = nlohmann::ordered_json;

int main() {
	json j;

	const char demo[] = "0123456789";
	j[string_view(demo, 1)] = "demo";
}

$ make
g++ main.cpp -Wall -std=c++17
In file included from main.cpp:1:
json.h: In instantiation of 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::value_type& nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::operator[](KeyType&&) [with KeyType = std::basic_string_view<char>; typename std::enable_if<typename std::conditional<((((typename nlohmann::detail::is_comparable<typename nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::object_comparator_t, const typename nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::object_t::key_type&, KeyType, void>::type::value && (!(true && std::is_same<typename std::remove_cv<typename std::remove_reference<_Tuple>::type>::type, typename nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::object_t::key_type>::value))) && ((! true) || typename nlohmann::detail::detector<nlohmann::detail::nonesuch, void, nlohmann::detail::detect_is_transparent, typename nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::object_comparator_t>::value_t::value)) && (! nlohmann::detail::is_json_iterator_of<nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>, typename std::remove_cv<typename std::remove_reference<_Tuple>::type>::type>::value)) && (! nlohmann::detail::is_specialization_of<nlohmann::json_pointer, typename std::remove_cv<typename std::remove_reference<typename std::remove_cv<typename std::remove_reference<_Tuple>::type>::type>::type>::type>::value)), std::integral_constant<bool, true>, std::integral_constant<bool, false> >::type::value, int>::type <anonymous> = 0; ObjectType = nlohmann::ordered_map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long long int; NumberUnsignedType = long long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::reference = nlohmann::basic_json<nlohmann::ordered_map>&]':
main.cpp:11:24:   required from here
json.h:20357:50: error: cannot convert 'std::basic_string_view<char>' to 'const key_type&' {aka 'const std::__cxx11::basic_string<char>&'}
20357 |             auto result = m_value.object->emplace(std::forward<KeyType>(key), nullptr);
      |                           ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from main.cpp:1:
json.h:18052:55: note:   initializing argument 1 of 'std::pair<typename std::vector<std::pair<const _Key, _Tp>, Allocator>::iterator, bool> nlohmann::ordered_map<Key, T, IgnoredLess, Allocator>::emplace(const key_type&, T&&) [with Key = std::__cxx11::basic_string<char>; T = nlohmann::basic_json<nlohmann::ordered_map>; IgnoredLess = std::less<void>; Allocator = std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::ordered_map> > >; typename std::vector<std::pair<const _Key, _Tp>, Allocator>::iterator = std::vector<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::ordered_map> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::ordered_map> > > >::iterator; nlohmann::ordered_map<Key, T, IgnoredLess, Allocator>::key_type = std::__cxx11::basic_string<char>]'
18052 |     std::pair<iterator, bool> emplace(const key_type& key, T&& t)
      | 

[falbrechtskirchinger]

That is currently only supported in the develop branch. If using that is not an option, you'll have to wait for the upcoming 3.11.0 release.

Edit: Since you mentioned ordered_json specifically, I double-checked and can confirm that there seems to be an issue. I'll investigate.
Edit 2: The problem is that I forgot to update the ordered_map implementation used by ordered_json to also accept types like string_view.

[fa66ot]

Hallo Florian, Ok, thank you for the info. Concerning the Edit 2, could you please advise, will it be fixed anytime soon?

[falbrechtskirchinger]

Hallo Florian, Ok, thank you for the info. Concerning the Edit 2, could you please advise, will it be fixed anytime soon?

I've implemented a fix. I just need to add unit tests and submit a PR. Very soon.

[falbrechtskirchinger]

The PR is up: #3564

[fa66ot]

Thank you very much!