make from_json SFINAE-correct

nlohmann · Sep 6, 2018 · 28d2376 · 28d2376
1 parent 9d0d291
commit 28d2376
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Showing 3 changed files with 10 additions and 50 deletions.
diff --git a/include/nlohmann/adl_serializer.hpp b/include/nlohmann/adl_serializer.hpp
@@ -20,8 +20,10 @@ struct adl_serializer
  @param[in,out] val value to write to
  */
  template<typename BasicJsonType, typename ValueType>
- static void from_json(BasicJsonType&& j, ValueType& val) noexcept(
- noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
+ static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
+ noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val))) -> decltype(
+ ::nlohmann::from_json(std::forward<BasicJsonType>(j), val)
+ )
  {
  ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
  }

diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
@@ -350,35 +350,13 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
 
 struct from_json_fn
 {
- private:
  template<typename BasicJsonType, typename T>
- auto call(const BasicJsonType& j, T& val, priority_tag<1> /*unused*/) const
+ auto operator()(const BasicJsonType& j, T& val) const
  noexcept(noexcept(from_json(j, val)))
  -> decltype(from_json(j, val), void())
  {
  return from_json(j, val);
  }
-
- template<typename BasicJsonType, typename T>
- void call(const BasicJsonType& /*unused*/, T& /*unused*/, priority_tag<0> /*unused*/) const noexcept
- {
- static_assert(sizeof(BasicJsonType) == 0,
- "could not find from_json() method in T's namespace");
-#ifdef _MSC_VER
- // MSVC does not show a stacktrace for the above assert
- using decayed = uncvref_t<T>;
- static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
- "forcing MSVC stacktrace to show which T we're talking about.");
-#endif
- }
-
- public:
- template<typename BasicJsonType, typename T>
- void operator()(const BasicJsonType& j, T& val) const
- noexcept(noexcept(std::declval<from_json_fn>().call(j, val, priority_tag<1> {})))
- {
- return call(j, val, priority_tag<1> {});
- }
 };
 }
 

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -1341,35 +1341,13 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
 
 struct from_json_fn
 {
- private:
  template<typename BasicJsonType, typename T>
- auto call(const BasicJsonType& j, T& val, priority_tag<1> /*unused*/) const
+ auto operator()(const BasicJsonType& j, T& val) const
  noexcept(noexcept(from_json(j, val)))
  -> decltype(from_json(j, val), void())
  {
  return from_json(j, val);
  }
-
- template<typename BasicJsonType, typename T>
- void call(const BasicJsonType& /*unused*/, T& /*unused*/, priority_tag<0> /*unused*/) const noexcept
- {
- static_assert(sizeof(BasicJsonType) == 0,
- "could not find from_json() method in T's namespace");
-#ifdef _MSC_VER
- // MSVC does not show a stacktrace for the above assert
- using decayed = uncvref_t<T>;
- static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
- "forcing MSVC stacktrace to show which T we're talking about.");
-#endif
- }
-
- public:
- template<typename BasicJsonType, typename T>
- void operator()(const BasicJsonType& j, T& val) const
- noexcept(noexcept(std::declval<from_json_fn>().call(j, val, priority_tag<1> {})))
- {
- return call(j, val, priority_tag<1> {});
- }
 };
 }
 
@@ -11109,8 +11087,10 @@ struct adl_serializer
  @param[in,out] val value to write to
  */
  template<typename BasicJsonType, typename ValueType>
- static void from_json(BasicJsonType&& j, ValueType& val) noexcept(
- noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val)))
+ static auto from_json(BasicJsonType&& j, ValueType& val) noexcept(
+ noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), val))) -> decltype(
+ ::nlohmann::from_json(std::forward<BasicJsonType>(j), val)
+ )
  {
  ::nlohmann::from_json(std::forward<BasicJsonType>(j), val);
  }