Using fifo_map

[adah1972]

The document says "you can specialize the object type with containers like tsl::ordered_map or nlohmann::fifo_map". I had a try with simple code like:

#include "fifo_map.hpp"
#include "json.hpp"

using json = nlohmann::basic_json<nlohmann::fifo_map>;

int main()
{
    json j;
}

It fails the compilation noisily. Would you please fix the issue, and/or clarify in the document how this should be done?

[nlohmann]

Can you please provide the compiler error messages?

[adah1972]

From GCC:

In file included from test.cpp:1:0:
fifo_map.hpp: In instantiation of 'nlohmann::fifo_map<Key, T, Compare, Allocator>::fifo_map() [with Key = std::__cxx11::basic_string<char>; T = nlohmann::basic_json<nlohmann::fifo_map>; Compare = std::less<std::__cxx11::basic_string<char> >; Allocator = std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map> > >]':
/usr/local/Cellar/gcc/6.3.0_1/include/c++/6.3.0/ext/new_allocator.h:120:4:   required from 'void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = nlohmann::fifo_map<std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map>, std::less<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map> > > >; _Args = {}; _Tp = nlohmann::fifo_map<std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map>, std::less<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map> > > >]'
json.hpp:1634:9:   required from 'static T* nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::create(Args&& ...) [with T = nlohmann::fifo_map<std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map>, std::less<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, nlohmann::basic_json<nlohmann::fifo_map> > > >; Args = {}; ObjectType = nlohmann::fifo_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'
json.hpp:1701:46:   required from 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::json_value::json_value(nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::value_t) [with ObjectType = nlohmann::fifo_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; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::value_t = nlohmann::detail::value_t]'
json.hpp:1917:49:   required from 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::basic_json(nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::value_t) [with ObjectType = nlohmann::fifo_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; nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::value_t = nlohmann::detail::value_t]'
json.hpp:1941:35:   required from 'nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer>::basic_json(std::nullptr_t) [with ObjectType = nlohmann::fifo_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; std::nullptr_t = std::nullptr_t]'
test.cpp:8:10:   required from here
fifo_map.hpp:126:63: error: no matching function for call to 'std::less<std::__cxx11::basic_string<char> >::less(std::unordered_map<std::__cxx11::basic_string<char>, long unsigned int, std::hash<std::__cxx11::basic_string<char> >, std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, long unsigned int> > >*)'
     fifo_map() : m_keys(), m_compare(&m_keys), m_map(m_compare) {}
                                                               ^

From Clang:

./fifo_map.hpp:126:28: fatal error: no matching constructor for initialization
      of 'std::__1::less<std::__1::basic_string<char> >'
    fifo_map() : m_keys(), m_compare(&m_keys), m_map(m_compare) {}
                           ^         ~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1740:31: note: 
      in instantiation of member function
      'nlohmann::fifo_map<std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>,
      std::__1::less<std::__1::basic_string<char> >,
      std::__1::allocator<std::__1::pair<const std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer> > > >::fifo_map' requested here
            ::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
                              ^
./json.hpp:1634:15: note: in instantiation of function template specialization
      'std::__1::allocator<nlohmann::fifo_map<std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>,
      std::__1::less<std::__1::basic_string<char> >,
      std::__1::allocator<std::__1::pair<const std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer> > > >
      >::construct<nlohmann::fifo_map<std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>,
      std::__1::less<std::__1::basic_string<char> >,
      std::__1::allocator<std::__1::pair<const std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer> > > >>' requested here
        alloc.construct(object.get(), std::forward<Args>(args)...);
              ^
./json.hpp:1701:30: note: in instantiation of function template specialization
      'nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator,
      adl_serializer>::create<nlohmann::fifo_map<std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>,
      std::__1::less<std::__1::basic_string<char> >,
      std::__1::allocator<std::__1::pair<const std::__1::basic_string<char>,
      nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer> > > >>' requested here
                    object = create<object_t>();
                             ^
./json.hpp:1917:31: note: in instantiation of member function
      'nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>::json_value::json_value' requested here
        : m_type(value_type), m_value(value_type)
                              ^
./json.hpp:1941:11: note: in instantiation of member function
      'nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>::basic_json' requested here
        : basic_json(value_t::null)
          ^
test.cpp:8:10: note: in instantiation of member function
      'nlohmann::basic_json<nlohmann::fifo_map, std::vector,
      std::__1::basic_string<char>, bool, long long, unsigned long long, double,
      std::allocator, adl_serializer>::basic_json' requested here
    json j;
         ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__functional_base:59:30: note: 
      candidate constructor (the implicit copy constructor) not viable: no known
      conversion from 'std::unordered_map<basic_string<char>, std::size_t> *'
      (aka 'unordered_map<std::__1::basic_string<char>, unsigned long> *') to
      'const std::__1::less<std::__1::basic_string<char> >' for 1st argument
struct _LIBCPP_TYPE_VIS_ONLY less : binary_function<_Tp, _Tp, bool>
                             ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__functional_base:59:30: note: 
      candidate constructor (the implicit move constructor) not viable: no known
      conversion from 'std::unordered_map<basic_string<char>, std::size_t> *'
      (aka 'unordered_map<std::__1::basic_string<char>, unsigned long> *') to
      'std::__1::less<std::__1::basic_string<char> >' for 1st argument
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__functional_base:59:30: note: 
      candidate constructor (the implicit default constructor) not viable:
      requires 0 arguments, but 1 was provided
1 error generated.

[nlohmann]

Thanks, I shall have a look.

[nlohmann]

I can confirm the error, but I have no idea how to fix it. I haven't tried fifo_map for this issue in a long time - I only mentioned it in the REAMDE, because I read somewhere that it was used successfully with this library. There may be issues, because fifo_map uses std::unordered_map internally, which is problematic (#164).

[arvidsson]

Using Visual Studio C++ 2017, I get the following error:
'add_key': is not a member of 'std::less'

[Daniel599]

Hi, I think I found out the problem, I think it's because when you are declaring object_t,
you use std::less, but not all map-like use std::less, i'm guessing it's because you wanted to set the allocator.
I can offer a patch:
Patch (might break people who set the map manually)
If you still want to keep you inner type allocator aware

template<class K, class V, class A>
using default_object_t = std::map<K, V, std::less< K >, A>; // A wrapper class for the new usage

template <
template<typename U, typename V, typename... Args> class ObjectType = default_object_t,
...
>
class basic_json
{
using object_t = ObjectType<StringType,
basic_json,
AllocatorType<std::pair<const StringType,
basic_json>>>; // Note I removed std::less
}

now if you want to use fifo_map you can by using the follow:

template<class K, class V, class A>
using my_obj = nlohmann::fifo_map<K, V, nlohmann::fifo_map_compare< K >, A>;

template<class K, class V, class A>
using my_obj2 = std::unordered_map<K, V, std::hash< K >, std::equal_to< K >, A>; // Can support also unordered_map

using my_json = nlohmann::basic_json<my_obj>;

please note that I haven't fully tested it, just basic example, not sure if it's the right way to do it, just an idea.

Also I can offer a workaround without changing the json library itself but it's a bit more ugly and will break if you will fix it using the patch above.

Let me know if you want this patch a pull request.

[donho]

Using Visual Studio C++ 2017, I get the following error:
'add_key': is not a member of 'std::less'

Same error under VS2015.
I think I will use nlohmann::json without fifo_map :(

[nlohmann]

Related to #660 (comment):

I really need to remove the hint to fifo_map from the documentation... :-(

[tomtachi]

Hmm. This is unfortunate as I would like to use fifo for improving the readability of json formatted file.

…

On 2017/09/10 23:24, Niels Lohmann wrote: Related to #660 (comment) <#660 (comment)>: I really need to remove the hint to fifo_map from the documentation... :-( — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#485 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ASymehOR4graqW5LASjgCRijQwJ5i-PJks5sg_E4gaJpZM4MU-ha>.

[tomtachi]

Hmm. This is unfortunate as I would like to use fifo for improving the human readability of json formatted file.

…

On 2017/09/10 23:24, Niels Lohmann wrote: Related to #660 (comment) <#660 (comment)>: I really need to remove the hint to fifo_map from the documentation... :-( — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#485 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ASymehOR4graqW5LASjgCRijQwJ5i-PJks5sg_E4gaJpZM4MU-ha>.

[SiebelsTim]

The fifo_map library uses an uncommon comparator type, which needs to hold a key storage. std::map for example uses std::less by default, which is a simple functor without state.
The json library follows the pattern of std::map which directly passes std::less<StringType> to the object type. And of course, there is no constructor for std::less<std::string>(std::unordered_map<Key, std::size_t>*). That's the problem.

It is not possible to solve this without breaking compatibility with one of the libraries.