Conversion from vector<bool> to json fails to build

[landler]

The following code:

#include "json.hpp"
#include <vector>
using nlohmann::json;

int main() {
	std::vector<bool> boolVector;
	json j;
	j["bool_vector"] = boolVector;
};

Fails to compile on os x (clang-800.0.42.1) when built like this:
clang++ -std=c++11 -c main.cpp

Substituting vector with another container (like list) compiles ok.

This also compiles fine on a linux system (I don't have the version info available, will update if necessary).

Am I missing some compiler params / something else or is this a problem with the library?

The full compilation error is below:

In file included from main.cpp:1:
./json.hpp:835:9: error: static_assert failed "could not find to_json() method in T's namespace"
        static_assert(sizeof(BasicJsonType) == 0,
        ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~
./json.hpp:844:16: note: in instantiation of function template specialization 'nlohmann::detail::to_json_fn::call<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long,
      unsigned long long, double, std::allocator, adl_serializer>, std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > > >' requested here
        return call(j, std::forward<T>(val), priority_tag<1> {});
               ^
./json.hpp:934:9: note: in instantiation of function template specialization 'nlohmann::detail::to_json_fn::operator()<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long,
      unsigned long long, double, std::allocator, adl_serializer>, std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > > >' requested here
        ::nlohmann::to_json(j, std::forward<ValueType>(val));
        ^
./json.hpp:1998:28: note: in instantiation of function template specialization 'nlohmann::adl_serializer<std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > >,
      void>::to_json<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long, unsigned long long, double, std::allocator, adl_serializer>,
      std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > > >' requested here
        JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
                           ^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:1740:31: note: in instantiation of function template specialization 'nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>,
      bool, long long, unsigned long long, double, std::allocator, adl_serializer>::basic_json<std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > >,
      std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > >, 0>' requested here
            ::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
                              ^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:1656:18: note: in instantiation of function template specialization 'std::__1::allocator<nlohmann::basic_json<std::map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double, std::allocator, adl_serializer> >::construct<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long
      long, unsigned long long, double, std::allocator, adl_serializer>, std::__1::__bit_const_reference<std::__1::vector<bool, std::__1::allocator<bool> > > >' requested here
            {__a.construct(__p, _VSTD::forward<_Args>(__args)...);}
                 ^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/memory:1502:14: note: (skipping 8 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
            {__construct(__has_construct<allocator_type, _Tp*, _Args...>(),
             ^
./json.hpp:829:16: note: in instantiation of function template specialization 'nlohmann::detail::to_json<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long, unsigned long
      long, double, std::allocator, adl_serializer>, std::__1::vector<bool, std::__1::allocator<bool> >, 0>' requested here
        return to_json(j, std::forward<T>(val));
               ^
./json.hpp:844:16: note: in instantiation of function template specialization 'nlohmann::detail::to_json_fn::call<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long,
      unsigned long long, double, std::allocator, adl_serializer>, std::__1::vector<bool, std::__1::allocator<bool> > &>' requested here
        return call(j, std::forward<T>(val), priority_tag<1> {});
               ^
./json.hpp:934:9: note: in instantiation of function template specialization 'nlohmann::detail::to_json_fn::operator()<nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long,
      unsigned long long, double, std::allocator, adl_serializer>, std::__1::vector<bool, std::__1::allocator<bool> > &>' requested here
        ::nlohmann::to_json(j, std::forward<ValueType>(val));
        ^
./json.hpp:1998:28: note: in instantiation of function template specialization 'nlohmann::adl_serializer<std::__1::vector<bool, std::__1::allocator<bool> >, void>::to_json<nlohmann::basic_json<std::map,
      std::vector, std::__1::basic_string<char>, bool, long long, unsigned long long, double, std::allocator, adl_serializer>, std::__1::vector<bool, std::__1::allocator<bool> > &>' requested here
        JSONSerializer<U>::to_json(*this, std::forward<CompatibleType>(val));
                           ^
main.cpp:8:21: note: in instantiation of function template specialization 'nlohmann::basic_json<std::map, std::vector, std::__1::basic_string<char>, bool, long long, unsigned long long, double, std::allocator,
      adl_serializer>::basic_json<std::__1::vector<bool, std::__1::allocator<bool> > &, std::__1::vector<bool, std::__1::allocator<bool> >, 0>' requested here
        j["bool_vector"] = boolVector;
                           ^
1 error generated.

[nlohmann]

I can confirm the issue with clang version 5.0.0 (trunk 296991) and gcc 7.0.1 20170305 (experimental).

[theodelrieu]

I forgot about that famous container ...
We need to add a from_json overload for vector<bool>

[nlohmann]

How was it excluded so far?

[gregmarr]

The problem is that a version of to_json/from_json that works for vector<T> doesn't necessarily work for vector<bool>.

[nlohmann]

I understand. I was just curious what part of the bool-magic breaks the requirements of the current from_json...

[TurpentineDistillery]

Usually problems with vector<bool> arise from the impossibility of having a pointer/reference to an element thereof... Wonder if that's the case here too.

[theodelrieu]

Exact, we iterate on container elements and call to_json on them.

Since vector<bool> iterators return proxy objects, it doesn't find the overload for those objects

[nlohmann]

Should be fixed with d9e2dd0. Waiting for Travis to complete.