Convert to Qt QVariant

[pylvain]

Hi, i'm currently working with JSON in Qt/Qml. Because of Qt poor support for JSON, i'm using this library. So, i have to convert this library's default type, which is using stl types, to a QVariant/QJsonValue, which is using Qt types, and vice versa. It's ok, but it feels like a waste of computer power and memory. Just out of curiosity, is it possible to work something out by modifying this definition :

template<template<typename U, typename V, typename... Args> class ObjectType =
         std::map,
         template<typename U, typename... Args> class ArrayType = std::vector,
         class StringType = std::string, class BooleanType = bool,
         class NumberIntegerType = std::int64_t,
         class NumberUnsignedType = std::uint64_t,
         class NumberFloatType = double,
         template<typename U> class AllocatorType = std::allocator,
         template<typename T, typename SFINAE = void> class JSONSerializer =
         adl_serializer,
         class BinaryType = std::vector<std::uint8_t>>
class basic_json;

with something like

class ObjectType = QJsonValue::Object
class StringType = QJsonValue::String 
etc ...

I'm no C++ expert, and i cannot make this work on my own, this is a bit too advanced for me.

Thanks

[ArtemSarmini]

Make your own alias like
using qt_json = basic_json<QMap, QVector, QString, ...>;
Do not try to edit library files.

[pylvain]

Thanks, simply that seems to work :

using myjson = basic_json<QMap,QVector,QString,bool,int,unsigned int,double>;

Silly me was trying to use QJSonValue:: thinking it was refering to types, but that was just an enum. Thank you !

[sandroandrade]

Thanks, simply that seems to work :

using myjson = basic_json<QMap,QVector,QString,bool,int,unsigned int,double>;

Silly me was trying to use QJSonValue:: thinking it was refering to types, but that was just an enum. Thank you !

Is this currently working? Using QVector as array type yelds the following error:

/usr/include/nlohmann/json.hpp:560:11: error: wrong number of template arguments (2, should be 1)
  560 |     using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
      |           ^~~~~~~

Probably because QVector doesn't support passing the allocator as template parameter. Any hint? Similar errors occur for QMap type.

Thanks in advance,

[nlohmann]

You could define a wrapper type that just consumes the AllocatorType argument. Something like

template<typename T, typename AllocatorType>
class q_vector_wrapper<T, AllocatorType> : public QVector<T>
{};

[Dariusz1989]

Can this be elaborated a bit? I want to support QVector etc etc but I'm hitting walls left and right.
Any hints? how to declare/how to use? etc?
Tried with :

namespace nlohmann {
    template<>
    struct adl_serializer<QString> {
        static void to_json(json &j, const QString &s) {
            j = s.toStdString();
        }

        static void from_json(const json &j, QString &s) {
            s = QString::fromStdString(j.get<std::string>());
        }
    };

    template<typename T>
    struct adl_serializer<QVector<T>> {
        static void to_json(json &j, const QVector<T> &data) {
            for (const auto &element: data) {
                j.push_back(element);
            }
        }

        static void from_json(const json &j, QVector<T> &data) {
            for (const auto &element: j) {
                data.push_back(element.get<T>());
            }
        }
    };
}

but lots of errors

error C2908: explicit specialization; 'nlohmann::json_abi_v3_11_2::adl_serializer<T,void>' has already been instantiated
        with
        [
            T=QString
        ]
        error C2766: explicit specialization; 'nlohmann::json_abi_v3_11_2::adl_serializer<T,void>' has already been defined
        with
        [
            T=QString
        ]
        : note: see previous definition of 'adl_serializer<QString,void>'
        ```
        etc etc