diff options
| -rw-r--r-- | lib/converters.h | 51 |
1 files changed, 39 insertions, 12 deletions
diff --git a/lib/converters.h b/lib/converters.h index 8ddf6e45..515c96fd 100644 --- a/lib/converters.h +++ b/lib/converters.h @@ -14,6 +14,7 @@ #include <QtCore/QUrlQuery> #include <QtCore/QVector> +#include <type_traits> #include <vector> class QVariant; @@ -21,10 +22,29 @@ class QVariant; namespace Quotient { template <typename T> struct JsonObjectConverter { - static void dumpTo(QJsonObject& jo, const T& pod) { jo = pod.toJson(); } - static void fillFrom(const QJsonObject& jo, T& pod) { pod = T(jo); } + // To be implemented in specialisations + static void dumpTo(QJsonObject&, const T&) = delete; + static void fillFrom(const QJsonObject&, T&) = delete; }; +namespace _impl { + template <typename T, typename = void> + struct JsonExporter { + static QJsonObject dump(const T& data) + { + QJsonObject jo; + JsonObjectConverter<T>::dumpTo(jo, data); + return jo; + } + }; + + template <typename T> + struct JsonExporter< + T, std::enable_if_t<std::is_invocable_v<decltype(&T::toJson), T>>> { + static auto dump(const T& data) { return data.toJson(); } + }; +} + //! \brief The switchboard for extra conversion algorithms behind from/toJson //! //! This template is mainly intended for partial conversion specialisations @@ -41,18 +61,25 @@ struct JsonObjectConverter { //! that they are not supported and it's not feasible to support those by means //! of overloading toJson() and specialising fromJson(). template <typename T> -struct JsonConverter { - static QJsonObject dump(const T& pod) - { - QJsonObject jo; - JsonObjectConverter<T>::dumpTo(jo, pod); - return jo; - } +struct JsonConverter : _impl::JsonExporter<T> { + // Unfortunately, if constexpr doesn't work with dump() and T::toJson + // because trying to check invocability of T::toJson hits a hard + // (non-SFINAE) compilation error if the member is not there. Hence a bit + // more verbose SFINAE construct in _impl::JsonExporter. + static T doLoad(const QJsonObject& jo) { - T pod; - JsonObjectConverter<T>::fillFrom(jo, pod); - return pod; + // 'else' below are required to suppress code generation for unused + // branches - 'return' is not enough + if constexpr (std::is_same_v<T, QJsonObject>) + return jo; + else if constexpr (std::is_constructible_v<T, QJsonObject>) + return T(jo); + else { + T pod; + JsonObjectConverter<T>::fillFrom(jo, pod); + return pod; + } } static T load(const QJsonValue& jv) { return doLoad(jv.toObject()); } static T load(const QJsonDocument& jd) { return doLoad(jd.object()); } |