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Commit 7dc268ef by Théo DELRIEU Committed by Théo DELRIEU
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add first version for alternate implementation

parent 4cdc61e4
Showing with 41 additions and 262 deletions
src/json.hpp
......@@ -106,17 +106,6 @@ SOFTWARE.
*/
namespace nlohmann
{
// TODO add real documentation before PR
// Traits structure declaration, users can specialize it for their own types
//
// constructing a json object from a user-defined type will call the
// 'json to_json(T)' function
//
// whereas calling json::get<T> will call 'T from_json(json const&)'
template <typename T, typename = void>
struct json_traits;
// alias templates to reduce boilerplate
template <bool B, typename T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
......@@ -166,64 +155,24 @@ void from_json();
struct to_json_fn
{
private:
// fallback overload
template <typename T>
static constexpr auto
impl(T &&val, long) noexcept(noexcept(to_json(std::forward<T>(val))))
constexpr auto
operator()(T &&val) const noexcept(noexcept(to_json(std::forward<T>(val))))
-> decltype(to_json(std::forward<T>(val)))
{
return to_json(std::forward<T>(val));
}
// preferred overload
template <typename T>
static constexpr auto impl(T &&val, int) noexcept(
noexcept(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val))))
-> decltype(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val)))
{
return json_traits<uncvref_t<T>>::to_json(std::forward<T>(val));
}
public:
template <typename T>
constexpr auto operator()(T &&val) const
noexcept(noexcept(to_json_fn::impl(std::forward<T>(val), 0)))
-> decltype(to_json_fn::impl(std::forward<T>(val), 0))
{
// decltype(0) -> int, so the compiler will try to take the 'preferred overload'
// if there is no specialization, the 'fallback overload' will be taken by converting 0 to long
return to_json_fn::impl(std::forward<T>(val), 0);
}
};
struct from_json_fn
{
private:
template <typename T, typename Json>
static constexpr auto impl(Json const &j, T &val,
long) noexcept(noexcept(from_json(j, val)))
-> decltype(from_json(j, val))
constexpr auto operator()(Json &&j, T &val) const
noexcept(noexcept(from_json(std::forward<Json>(j), val)))
-> decltype(from_json(std::forward<Json>(j), val))
{
return from_json(j, val);
}
template <typename T, typename Json>
static constexpr auto
impl(Json const &j, T &val,
int) noexcept(noexcept(json_traits<T>::from_json(j, val)))
-> decltype(json_traits<T>::from_json(j, val))
{
return json_traits<T>::from_json(j, val);
}
public:
template <typename T, typename Json>
constexpr auto operator()(Json const &j, T &val) const
noexcept(noexcept(from_json_fn::impl(j, val, 0)))
-> decltype(from_json_fn::impl(j, val, 0))
{
return from_json_fn::impl(j, val, 0);
return from_json(std::forward<Json>(j), val);
}
};
......@@ -265,6 +214,32 @@ inline namespace
constexpr auto const& from_json = _static_const<detail::from_json_fn>::value;
}
// default JSONSerializer template argument
// will use ADL for serialization
struct adl_serializer
{
template <typename T, typename Json, typename = enable_if_t<std::is_default_constructible<uncvref_t<T>>::value>>
static auto from_json(Json&& j) -> uncvref_t<decltype(::nlohmann::from_json(std::forward<Json>(j), std::declval<T&>()), std::declval<T>())>
{
uncvref_t<T> ret;
::nlohmann::from_json(std::forward<Json>(j), ret);
return ret;
}
template <typename T, typename Json>
static auto from_json(Json&& j, T& val) -> decltype(::nlohmann::from_json(std::forward<Json>(j), val))
{
::nlohmann::from_json(std::forward<Json>(j), val);
}
template <typename T>
static auto to_json(T&& val) -> decltype(::nlohmann::to_json(std::forward<T>(val)))
{
return ::nlohmann::to_json(std::forward<T>(val));
}
};
/*!
@brief a class to store JSON values
......@@ -352,7 +327,8 @@ template <
class NumberIntegerType = std::int64_t,
class NumberUnsignedType = std::uint64_t,
class NumberFloatType = double,
template<typename U> class AllocatorType = std::allocator
template<typename U> class AllocatorType = std::allocator,
class JSONSerializer = adl_serializer
>
class basic_json
{
......@@ -1421,30 +1397,10 @@ class basic_json
assert_invariant();
}
// constructor chosen for user-defined types that either have:
// - a to_json free function in their type's namespace
// - a json_traits specialization for their type
//
// If there is both a free function and a specialization, the latter will be chosen,
// since it is a more advanced use
//
// note: constructor is marked explicit to avoid the following issue:
//
// struct not_equality_comparable{};
//
// not_equality_comparable{} == not_equality_comparable{};
//
// this will construct implicitely 2 json objects and call operator== on them
// which can cause nasty bugs on the user's in json-unrelated code
//
// the trade-off is expressiveness in initializer-lists
// auto j = json{{"a", json(not_equality_comparable{})}};
//
// we can remove this constraint though, since lots of ctor are not explicit already
template <typename T, typename = decltype(::nlohmann::to_json(
std::declval<uncvref_t<T>>()))>
// constructor chosen when JSONSerializer::to_json exists for type T
template <typename T, typename = decltype(JSONSerializer::to_json(std::declval<uncvref_t<T>>()))>
explicit basic_json(T &&val)
: basic_json(::nlohmann::to_json(std::forward<T>(val))) {}
: basic_json(JSONSerializer::to_json(std::forward<T>(val))) {}
/*!
@brief create a string (explicit)
......@@ -3115,16 +3071,11 @@ class basic_json
return get_impl(static_cast<ValueType*>(nullptr));
}
template <typename ValueType>
auto get() const -> remove_reference_t<
decltype(::nlohmann::from_json(*this, std::declval<ValueType &>()),
std::declval<ValueType>())>
template <typename ValueType, typename = enable_if_t<std::is_default_constructible<uncvref_t<ValueType>>::value, float>>
auto get() const -> remove_reference_t<decltype(JSONSerializer::from_json(*this, std::declval<ValueType&>()), std::declval<ValueType>())>
{
static_assert(std::is_default_constructible<ValueType>::value,
"ValueType must be default-constructible when user-defined "
"from_json method is used");
ValueType ret;
::nlohmann::from_json(*this, ret);
uncvref_t<ValueType> ret;
JSONSerializer::from_json(*this, ret);
return ret;
}
......
test/src/unit-constructor3.cpp
......@@ -35,9 +35,6 @@ using nlohmann::json;
namespace udt
{
// only used by counter_type
auto nb_free_function_calls = 0;
struct empty_type {};
struct pod_type {
int a;
......@@ -51,10 +48,6 @@ struct bit_more_complex_type {
std::string c;
};
struct counter_type
{
};
// best optional implementation ever
template <typename T>
class optional_type
......@@ -75,11 +68,6 @@ private:
std::shared_ptr<T> _val;
};
struct no_json_traits_type
{
int a;
};
// free to/from_json functions
json to_json(empty_type)
......@@ -107,17 +95,6 @@ json to_json(optional_type<T> const& opt)
return json(*opt);
}
json to_json(no_json_traits_type const& p)
{
return {{"a", p.a}};
}
json to_json(counter_type)
{
++nb_free_function_calls;
return json::object();
}
void from_json(json const&j, empty_type& t)
{
assert(j.empty());
......@@ -136,11 +113,6 @@ void from_json(json const&j, bit_more_complex_type& t)
j["c"].get<std::string>()};
}
void from_json(json const& j, no_json_traits_type& t)
{
t.a = j["a"].get<int>();
}
template <typename T>
void from_json(json const& j, optional_type<T>& t)
{
......@@ -150,11 +122,6 @@ void from_json(json const& j, optional_type<T>& t)
t = j.get<T>();
}
void from_json(json const&, counter_type&)
{
++nb_free_function_calls;
}
inline bool operator==(pod_type const& lhs, pod_type const& rhs) noexcept
{
return std::tie(lhs.a, lhs.b, lhs.c) == std::tie(rhs.a, rhs.b, rhs.c);
......@@ -174,107 +141,8 @@ inline bool operator==(optional_type<T> const& lhs, optional_type<T> const& rhs)
return false;
return *lhs == *rhs;
}
inline bool operator==(no_json_traits_type const& lhs, no_json_traits_type const& rhs)
{
return lhs.a == rhs.a;
}
}
namespace nlohmann
{
template <>
struct json_traits<udt::empty_type>
{
using type = udt::empty_type;
static json to_json(type)
{
return json::object();
}
static type from_json(json const& j)
{
assert(j.is_object() and j.empty());
return {};
}
};
template <>
struct json_traits<udt::pod_type>
{
using type = udt::pod_type;
static json to_json(type const& t)
{
return {{"a", t.a}, {"b", t.b}, {"c", t.c}};
}
static type from_json(json const& j)
{
assert(j.is_object());
return {j["a"].get<int>(), j["b"].get<char>(), j["c"].get<short>()};
}
};
template <>
struct json_traits<udt::bit_more_complex_type>
{
using type = udt::bit_more_complex_type;
static json to_json(type const& t)
{
return json{{"a", json{t.a}}, {"b", json{t.b}}, {"c", t.c}};
}
static type from_json(json const& j)
{
return {j["a"].get<udt::pod_type>(), j["b"].get<udt::pod_type>(),
j["c"].get<std::string>()};
}
};
template <typename T>
struct json_traits<udt::optional_type<T>>
{
using type = udt::optional_type<T>;
static json to_json(type const& t)
{
if (t)
return json(*t);
return {};
}
static type from_json(json const& j)
{
if (j.is_null())
return {};
return type{j.get<T>()};
}
};
template <>
struct json_traits<udt::counter_type>
{
using type = udt::counter_type;
static int nb_calls;
static json to_json(type)
{
++nb_calls;
return json::object();
}
static void from_json(json const&, type&)
{
++nb_calls;
}
};
int json_traits<udt::counter_type>::nb_calls{0};
}
TEST_CASE("constructors for user-defined types", "[udt]")
{
SECTION("empty type")
......@@ -415,24 +283,6 @@ TEST_CASE("get<> for user-defined types", "[udt]")
CHECK(*v == expected);
}
}
SECTION("no json_traits specialization, use of ADL")
{
udt::no_json_traits_type val{42};
auto const expected = json{{"a", 42}};
auto const j = json(val);
CHECK(j == expected);
}
SECTION("counter_type")
{
// check that the traits specialization is chosen
auto const j = json{udt::counter_type{}};
CHECK(nlohmann::json_traits<udt::counter_type>::nb_calls == 1);
auto const elem = j.get<udt::counter_type>();
CHECK(nlohmann::json_traits<udt::counter_type>::nb_calls == 2);
CHECK(udt::nb_free_function_calls == 0);
}
}
TEST_CASE("to_json free function", "[udt]")
......@@ -477,16 +327,6 @@ TEST_CASE("to_json free function", "[udt]")
CHECK(expected == j);
}
}
SECTION("no json_traits specialization")
{
udt::no_json_traits_type t{42};
json expected;
expected["a"] = 42;
auto const j = nlohmann::to_json(t);
CHECK(j == expected);
}
}
TEST_CASE("from_json free function", "[udt]")
......@@ -535,16 +375,4 @@ TEST_CASE("from_json free function", "[udt]")
CHECK(expected == o);
}
}
SECTION("no json_traits specialization")
{
udt::no_json_traits_type expected{42};
udt::no_json_traits_type res;
auto const j = json{{"a", 42}};
nlohmann::from_json(j, res);
CHECK(res == expected);
res = j.get<udt::no_json_traits_type>();
CHECK(res == expected);
}
}
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