j3d1/json
1
0
Fork 0
Code Issues Pull requests Releases Wiki Activity

use a priority_tag instead of int and longs with sfinae-dispatch

Browse source
This commit is contained in:
Théo DELRIEU 2017-01-14 02:33:03 +01:00
parent b8012876a5
commit 63e4249e9f
1 changed files with 16 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
src/json.hpp
View file

@ -189,6 +189,11 @@ template <typename Json> std::string type_name(Json const &j)
} }
} }
// dispatch utility (taken from ranges-v3)
template <unsigned N> struct priority_tag : priority_tag<N - 1> {};
template <> struct priority_tag<0> {};
// This is an experiment. I need this to move constructors out of basic_json. // This is an experiment. I need this to move constructors out of basic_json.
// I'm sure there is a better way, but this might need a big basic_json refactoring // I'm sure there is a better way, but this might need a big basic_json refactoring
template <value_t> struct external_constructor; template <value_t> struct external_constructor;
@ -642,9 +647,8 @@ void from_json(Json const&j, std::forward_list<T, Allocator>& l)
l.push_front(it->template get<T>()); l.push_front(it->template get<T>());
} }
template <typename Json, typename CompatibleArrayType> template <typename Json, typename CompatibleArrayType>
void from_json_array_impl(Json const &j, CompatibleArrayType &arr, long) void from_json_array_impl(Json const &j, CompatibleArrayType &arr, priority_tag<0>)
{ {
using std::begin; using std::begin;
using std::end; using std::end;
@ -659,7 +663,7 @@ void from_json_array_impl(Json const &j, CompatibleArrayType &arr, long)
} }
template <typename Json, typename CompatibleArrayType> template <typename Json, typename CompatibleArrayType>
auto from_json_array_impl(Json const &j, CompatibleArrayType &arr, int) auto from_json_array_impl(Json const &j, CompatibleArrayType &arr, priority_tag<1>)
-> decltype( -> decltype(
arr.reserve(std::declval<typename CompatibleArrayType::size_type>()), arr.reserve(std::declval<typename CompatibleArrayType::size_type>()),
void()) void())
@ -693,7 +697,7 @@ void from_json(Json const &j, CompatibleArrayType &arr)
if (!j.is_array()) if (!j.is_array())
throw std::domain_error("type must be array, but is " + type_name(j)); throw std::domain_error("type must be array, but is " + type_name(j));
} }
from_json_array_impl(j, arr, 0); from_json_array_impl(j, arr, priority_tag<1>{});
} }
@ -744,7 +748,7 @@ void from_json(Json const &j, ArithmeticType &val)
struct to_json_fn struct to_json_fn
{ {
template <typename Json, typename T> template <typename Json, typename T>
auto call(int, Json& j, T&& val) const auto call(Json& j, T&& val, priority_tag<1>) const
noexcept(noexcept(to_json(j, std::forward<T>(val)))) noexcept(noexcept(to_json(j, std::forward<T>(val))))
-> decltype(to_json(j, std::forward<T>(val)), -> decltype(to_json(j, std::forward<T>(val)),
void()) void())
@ -753,7 +757,7 @@ struct to_json_fn
} }
template <typename Json, typename T> template <typename Json, typename T>
void call(long, Json&, T&&) const noexcept void call(Json&, T&&, priority_tag<0>) const noexcept
{ {
static_assert(sizeof(Json) == 0, "to_json method in T's namespace can not be called"); static_assert(sizeof(Json) == 0, "to_json method in T's namespace can not be called");
} }
@ -761,9 +765,9 @@ struct to_json_fn
public: public:
template <typename Json, typename T> template <typename Json, typename T>
void operator()(Json &j, T &&val) const void operator()(Json &j, T &&val) const
noexcept(noexcept(std::declval<to_json_fn>().call(0, j, std::forward<T>(val)))) noexcept(noexcept(std::declval<to_json_fn>().call(j, std::forward<T>(val), priority_tag<1>{})))
{ {
return call(0, j, std::forward<T>(val)); return call(j, std::forward<T>(val), priority_tag<1>{});
} }
}; };
@ -771,7 +775,7 @@ struct from_json_fn
{ {
private: private:
template <typename Json, typename T> template <typename Json, typename T>
auto call(int, Json const &j, T &val) const auto call(Json const &j, T &val, priority_tag<1>) const
noexcept(noexcept(from_json(j, val))) noexcept(noexcept(from_json(j, val)))
-> decltype(from_json(j, val), void()) -> decltype(from_json(j, val), void())
{ {
@ -779,7 +783,7 @@ private:
} }
template <typename Json, typename T> template <typename Json, typename T>
void call(long, Json const&, T&) const noexcept void call(Json const&, T&, priority_tag<0>) const noexcept
{ {
static_assert(sizeof(Json) == 0, "from_json method in T's namespace can not be called"); static_assert(sizeof(Json) == 0, "from_json method in T's namespace can not be called");
} }
@ -787,9 +791,9 @@ private:
public: public:
template <typename Json, typename T> template <typename Json, typename T>
void operator()(Json const &j, T &val) const void operator()(Json const &j, T &val) const
noexcept(noexcept(std::declval<from_json_fn>().call(0, j, val))) noexcept(noexcept(std::declval<from_json_fn>().call(j, val, priority_tag<1>{})))
{ {
return call(0, j, val); return call(j, val, priority_tag<1>{});
} }
}; };