mirror of
https://github.com/nlohmann/json
synced 2024-11-27 22:30:09 +00:00
add first version for alternate implementation
This commit is contained in:
Théo DELRIEU
Théo DELRIEU
parent
4cdc61e493
commit
7dc268ef42
131
src/json.hpp
131
src/json.hpp
@ -106,17 +106,6 @@ SOFTWARE.
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*/
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namespace nlohmann
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{
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// TODO add real documentation before PR
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// Traits structure declaration, users can specialize it for their own types
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//
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// constructing a json object from a user-defined type will call the
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// 'json to_json(T)' function
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//
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// whereas calling json::get<T> will call 'T from_json(json const&)'
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template <typename T, typename = void>
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struct json_traits;
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// alias templates to reduce boilerplate
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template <bool B, typename T = void>
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using enable_if_t = typename std::enable_if<B, T>::type;
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@ -166,64 +155,24 @@ void from_json();
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struct to_json_fn
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{
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private:
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// fallback overload
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template <typename T>
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static constexpr auto
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impl(T &&val, long) noexcept(noexcept(to_json(std::forward<T>(val))))
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constexpr auto
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operator()(T &&val) const noexcept(noexcept(to_json(std::forward<T>(val))))
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-> decltype(to_json(std::forward<T>(val)))
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{
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return to_json(std::forward<T>(val));
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}
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// preferred overload
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template <typename T>
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static constexpr auto impl(T &&val, int) noexcept(
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noexcept(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val))))
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-> decltype(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val)))
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{
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return json_traits<uncvref_t<T>>::to_json(std::forward<T>(val));
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}
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public:
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template <typename T>
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constexpr auto operator()(T &&val) const
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noexcept(noexcept(to_json_fn::impl(std::forward<T>(val), 0)))
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-> decltype(to_json_fn::impl(std::forward<T>(val), 0))
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{
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// decltype(0) -> int, so the compiler will try to take the 'preferred overload'
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// if there is no specialization, the 'fallback overload' will be taken by converting 0 to long
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return to_json_fn::impl(std::forward<T>(val), 0);
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}
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};
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struct from_json_fn
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{
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private:
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template <typename T, typename Json>
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static constexpr auto impl(Json const &j, T &val,
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long) noexcept(noexcept(from_json(j, val)))
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-> decltype(from_json(j, val))
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constexpr auto operator()(Json &&j, T &val) const
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noexcept(noexcept(from_json(std::forward<Json>(j), val)))
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-> decltype(from_json(std::forward<Json>(j), val))
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{
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return from_json(j, val);
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}
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template <typename T, typename Json>
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static constexpr auto
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impl(Json const &j, T &val,
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int) noexcept(noexcept(json_traits<T>::from_json(j, val)))
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-> decltype(json_traits<T>::from_json(j, val))
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{
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return json_traits<T>::from_json(j, val);
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}
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public:
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template <typename T, typename Json>
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constexpr auto operator()(Json const &j, T &val) const
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noexcept(noexcept(from_json_fn::impl(j, val, 0)))
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-> decltype(from_json_fn::impl(j, val, 0))
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{
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return from_json_fn::impl(j, val, 0);
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return from_json(std::forward<Json>(j), val);
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}
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};
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@ -265,6 +214,32 @@ inline namespace
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constexpr auto const& from_json = _static_const<detail::from_json_fn>::value;
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}
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// default JSONSerializer template argument
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// will use ADL for serialization
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struct adl_serializer
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{
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template <typename T, typename Json, typename = enable_if_t<std::is_default_constructible<uncvref_t<T>>::value>>
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static auto from_json(Json&& j) -> uncvref_t<decltype(::nlohmann::from_json(std::forward<Json>(j), std::declval<T&>()), std::declval<T>())>
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{
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uncvref_t<T> ret;
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::nlohmann::from_json(std::forward<Json>(j), ret);
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return ret;
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}
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template <typename T, typename Json>
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static auto from_json(Json&& j, T& val) -> decltype(::nlohmann::from_json(std::forward<Json>(j), val))
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{
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::nlohmann::from_json(std::forward<Json>(j), val);
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}
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template <typename T>
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static auto to_json(T&& val) -> decltype(::nlohmann::to_json(std::forward<T>(val)))
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{
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return ::nlohmann::to_json(std::forward<T>(val));
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}
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};
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/*!
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@brief a class to store JSON values
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@ -352,7 +327,8 @@ template <
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class NumberIntegerType = std::int64_t,
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class NumberUnsignedType = std::uint64_t,
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class NumberFloatType = double,
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template<typename U> class AllocatorType = std::allocator
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template<typename U> class AllocatorType = std::allocator,
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class JSONSerializer = adl_serializer
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>
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class basic_json
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{
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@ -1421,30 +1397,10 @@ class basic_json
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assert_invariant();
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}
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// constructor chosen for user-defined types that either have:
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// - a to_json free function in their type's namespace
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// - a json_traits specialization for their type
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//
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// If there is both a free function and a specialization, the latter will be chosen,
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// since it is a more advanced use
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//
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// note: constructor is marked explicit to avoid the following issue:
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//
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// struct not_equality_comparable{};
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//
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// not_equality_comparable{} == not_equality_comparable{};
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//
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// this will construct implicitely 2 json objects and call operator== on them
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// which can cause nasty bugs on the user's in json-unrelated code
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//
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// the trade-off is expressiveness in initializer-lists
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// auto j = json{{"a", json(not_equality_comparable{})}};
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//
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// we can remove this constraint though, since lots of ctor are not explicit already
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template <typename T, typename = decltype(::nlohmann::to_json(
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std::declval<uncvref_t<T>>()))>
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// constructor chosen when JSONSerializer::to_json exists for type T
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template <typename T, typename = decltype(JSONSerializer::to_json(std::declval<uncvref_t<T>>()))>
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explicit basic_json(T &&val)
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: basic_json(::nlohmann::to_json(std::forward<T>(val))) {}
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: basic_json(JSONSerializer::to_json(std::forward<T>(val))) {}
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/*!
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@brief create a string (explicit)
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@ -3115,16 +3071,11 @@ class basic_json
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return get_impl(static_cast<ValueType*>(nullptr));
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}
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template <typename ValueType>
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auto get() const -> remove_reference_t<
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decltype(::nlohmann::from_json(*this, std::declval<ValueType &>()),
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std::declval<ValueType>())>
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template <typename ValueType, typename = enable_if_t<std::is_default_constructible<uncvref_t<ValueType>>::value, float>>
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auto get() const -> remove_reference_t<decltype(JSONSerializer::from_json(*this, std::declval<ValueType&>()), std::declval<ValueType>())>
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{
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static_assert(std::is_default_constructible<ValueType>::value,
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"ValueType must be default-constructible when user-defined "
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"from_json method is used");
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ValueType ret;
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::nlohmann::from_json(*this, ret);
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uncvref_t<ValueType> ret;
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JSONSerializer::from_json(*this, ret);
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return ret;
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}
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@ -35,9 +35,6 @@ using nlohmann::json;
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namespace udt
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{
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// only used by counter_type
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auto nb_free_function_calls = 0;
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struct empty_type {};
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struct pod_type {
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int a;
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@ -51,10 +48,6 @@ struct bit_more_complex_type {
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std::string c;
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};
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struct counter_type
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{
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};
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// best optional implementation ever
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template <typename T>
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class optional_type
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@ -75,11 +68,6 @@ private:
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std::shared_ptr<T> _val;
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};
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struct no_json_traits_type
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{
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int a;
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};
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// free to/from_json functions
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json to_json(empty_type)
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@ -107,17 +95,6 @@ json to_json(optional_type<T> const& opt)
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return json(*opt);
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}
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json to_json(no_json_traits_type const& p)
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{
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return {{"a", p.a}};
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}
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json to_json(counter_type)
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{
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++nb_free_function_calls;
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return json::object();
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}
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void from_json(json const&j, empty_type& t)
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{
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assert(j.empty());
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@ -136,11 +113,6 @@ void from_json(json const&j, bit_more_complex_type& t)
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j["c"].get<std::string>()};
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}
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void from_json(json const& j, no_json_traits_type& t)
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{
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t.a = j["a"].get<int>();
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}
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template <typename T>
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void from_json(json const& j, optional_type<T>& t)
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{
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@ -150,11 +122,6 @@ void from_json(json const& j, optional_type<T>& t)
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t = j.get<T>();
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}
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void from_json(json const&, counter_type&)
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{
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++nb_free_function_calls;
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}
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inline bool operator==(pod_type const& lhs, pod_type const& rhs) noexcept
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{
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return std::tie(lhs.a, lhs.b, lhs.c) == std::tie(rhs.a, rhs.b, rhs.c);
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@ -174,106 +141,7 @@ inline bool operator==(optional_type<T> const& lhs, optional_type<T> const& rhs)
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return false;
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return *lhs == *rhs;
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}
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inline bool operator==(no_json_traits_type const& lhs, no_json_traits_type const& rhs)
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{
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return lhs.a == rhs.a;
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}
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}
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namespace nlohmann
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{
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template <>
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struct json_traits<udt::empty_type>
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{
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using type = udt::empty_type;
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static json to_json(type)
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{
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return json::object();
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}
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static type from_json(json const& j)
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{
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assert(j.is_object() and j.empty());
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return {};
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}
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};
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template <>
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struct json_traits<udt::pod_type>
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{
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using type = udt::pod_type;
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static json to_json(type const& t)
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{
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return {{"a", t.a}, {"b", t.b}, {"c", t.c}};
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}
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static type from_json(json const& j)
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{
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assert(j.is_object());
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return {j["a"].get<int>(), j["b"].get<char>(), j["c"].get<short>()};
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}
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};
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template <>
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struct json_traits<udt::bit_more_complex_type>
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{
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using type = udt::bit_more_complex_type;
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static json to_json(type const& t)
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{
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return json{{"a", json{t.a}}, {"b", json{t.b}}, {"c", t.c}};
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}
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static type from_json(json const& j)
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{
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return {j["a"].get<udt::pod_type>(), j["b"].get<udt::pod_type>(),
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j["c"].get<std::string>()};
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}
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};
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template <typename T>
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struct json_traits<udt::optional_type<T>>
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{
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using type = udt::optional_type<T>;
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static json to_json(type const& t)
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{
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if (t)
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return json(*t);
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return {};
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}
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static type from_json(json const& j)
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{
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if (j.is_null())
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return {};
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return type{j.get<T>()};
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}
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};
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template <>
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struct json_traits<udt::counter_type>
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{
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using type = udt::counter_type;
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static int nb_calls;
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static json to_json(type)
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{
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++nb_calls;
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return json::object();
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}
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static void from_json(json const&, type&)
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{
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++nb_calls;
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}
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};
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int json_traits<udt::counter_type>::nb_calls{0};
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}
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TEST_CASE("constructors for user-defined types", "[udt]")
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{
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@ -415,24 +283,6 @@ TEST_CASE("get<> for user-defined types", "[udt]")
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CHECK(*v == expected);
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}
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}
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SECTION("no json_traits specialization, use of ADL")
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{
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udt::no_json_traits_type val{42};
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auto const expected = json{{"a", 42}};
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auto const j = json(val);
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CHECK(j == expected);
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}
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SECTION("counter_type")
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{
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// check that the traits specialization is chosen
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auto const j = json{udt::counter_type{}};
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CHECK(nlohmann::json_traits<udt::counter_type>::nb_calls == 1);
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auto const elem = j.get<udt::counter_type>();
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CHECK(nlohmann::json_traits<udt::counter_type>::nb_calls == 2);
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CHECK(udt::nb_free_function_calls == 0);
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}
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}
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TEST_CASE("to_json free function", "[udt]")
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@ -477,16 +327,6 @@ TEST_CASE("to_json free function", "[udt]")
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CHECK(expected == j);
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}
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}
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SECTION("no json_traits specialization")
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{
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udt::no_json_traits_type t{42};
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json expected;
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expected["a"] = 42;
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auto const j = nlohmann::to_json(t);
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CHECK(j == expected);
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}
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}
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TEST_CASE("from_json free function", "[udt]")
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@ -535,16 +375,4 @@ TEST_CASE("from_json free function", "[udt]")
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CHECK(expected == o);
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}
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}
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SECTION("no json_traits specialization")
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{
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udt::no_json_traits_type expected{42};
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udt::no_json_traits_type res;
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auto const j = json{{"a", 42}};
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nlohmann::from_json(j, res);
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CHECK(res == expected);
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res = j.get<udt::no_json_traits_type>();
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CHECK(res == expected);
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}
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}
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