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remove has_destructor and has_json_traits, use decltype instead

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This commit is contained in:
Théo DELRIEU 2016-10-20 18:02:07 +02:00
parent 12b4555b13
commit 03b391c37b
1 changed files with 12 additions and 33 deletions
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45
src/json.hpp
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@ -161,26 +161,6 @@ struct has_mapped_type
std::is_integral<decltype(detect(std::declval<T>()))>::value; std::is_integral<decltype(detect(std::declval<T>()))>::value;
}; };
// taken from http://stackoverflow.com/questions/10711952/how-to-detect-existence-of-a-class-using-sfinae
// used to determine if json_traits is defined for a given type T
template <typename T>
struct has_destructor
{
template <typename U>
static std::true_type detect(decltype(std::declval<U>().~U())*);
template <typename>
static std::false_type detect(...);
static constexpr bool value = decltype(detect<T>(0))::value;
};
template<typename T>
struct has_json_traits
{
static constexpr bool value = has_destructor<json_traits<T>>::value;
};
struct to_json_fn struct to_json_fn
{ {
template <typename T> template <typename T>
@ -1407,8 +1387,7 @@ class basic_json
// auto j = json{{"a", json(not_equality_comparable{})}}; // auto j = json{{"a", json(not_equality_comparable{})}};
// //
// we can remove this constraint though, since lots of ctor are not explicit already // we can remove this constraint though, since lots of ctor are not explicit already
template <typename T, typename = enable_if_t< template <typename T, typename = decltype(json_traits<uncvref_t<T>>::to_json(std::declval<uncvref_t<T>>()))>
detail::has_json_traits<uncvref_t<T>>::value>>
explicit basic_json(T &&val) explicit basic_json(T &&val)
: basic_json(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val))) : basic_json(json_traits<uncvref_t<T>>::to_json(std::forward<T>(val)))
{ {
@ -2775,24 +2754,19 @@ class basic_json
// get_impl overload chosen if json_traits struct is specialized for type T // get_impl overload chosen if json_traits struct is specialized for type T
// simply returns json_traits<T>::from_json(*this); // simply returns json_traits<T>::from_json(*this);
template <typename T, typename = enable_if_t< // dual argument to avoid conflicting with get_impl overloads taking a pointer
detail::has_json_traits<uncvref_t<T>>::value>> template <typename T>
auto get_impl(T *) const -> decltype( auto get_impl(int, int) const -> decltype(json_traits<uncvref_t<T>>::from_json(*this))
json_traits<uncvref_t<T>>::from_json(std::declval<basic_json>()))
{ {
return json_traits<uncvref_t<T>>::from_json(*this); return json_traits<uncvref_t<T>>::from_json(*this);
} }
// this one is quite atrocious
// this overload is chosen ONLY if json_traits struct is not specialized, and if the expression nlohmann::from_json(*this, T&) is valid // this overload is chosen ONLY if json_traits struct is not specialized, and if the expression nlohmann::from_json(*this, T&) is valid
// I chose to prefer the json_traits specialization if it exists, since it's a more advanced use. // I chose to prefer the json_traits specialization if it exists, since it's a more advanced use.
// But we can of course change this behaviour // But we can of course change this behaviour
template <typename T> template <typename T>
auto get_impl(T *) const -> enable_if_t< auto get_impl(long, long) const -> uncvref_t<decltype(::nlohmann::from_json(*this, std::declval<T &>()),
not detail::has_json_traits<remove_cv_t<T>>::value, std::declval<T>())>
uncvref_t<decltype(::nlohmann::from_json(std::declval<basic_json>(),
std::declval<T &>()),
std::declval<T>())>>
{ {
remove_cv_t<T> ret; remove_cv_t<T> ret;
// I guess this output parameter is the only way to get ADL // I guess this output parameter is the only way to get ADL
@ -3108,11 +3082,16 @@ class basic_json
*/ */
template<typename ValueType, typename std::enable_if< template<typename ValueType, typename std::enable_if<
not std::is_pointer<ValueType>::value, int>::type = 0> not std::is_pointer<ValueType>::value, int>::type = 0>
ValueType get() const auto get() const -> decltype(get_impl(static_cast<ValueType*>(nullptr)))
{ {
return get_impl(static_cast<ValueType*>(nullptr)); return get_impl(static_cast<ValueType*>(nullptr));
} }
template <typename ValueType>
auto get() const -> decltype(get_impl<ValueType>(0, 0))
{
return get_impl<ValueType>(0, 0);
}
/*! /*!
@brief get a pointer value (explicit) @brief get a pointer value (explicit)