Re-add value_type detection to distinguish string types (#3604)

* Re-add value_type detection to is_constructible_string_type trait * Add value_type detection to from_json for strings
nlohmann · Jul 28, 2022 · a87c188 · a87c188
1 parent a714381
commit a87c188
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Showing 3 changed files with 10 additions and 4 deletions.
diff --git a/include/nlohmann/detail/conversions/from_json.hpp b/include/nlohmann/detail/conversions/from_json.hpp
@@ -117,6 +117,7 @@ template <
     typename BasicJsonType, typename StringType,
     enable_if_t <
         std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
+        && is_detected_exact<typename BasicJsonType::string_t::value_type, value_type_t, StringType>::value
         && !std::is_same<typename BasicJsonType::string_t, StringType>::value
         && !is_json_ref<StringType>::value, int > = 0 >
 inline void from_json(const BasicJsonType& j, StringType& s)

diff --git a/include/nlohmann/detail/meta/type_traits.hpp b/include/nlohmann/detail/meta/type_traits.hpp
@@ -363,8 +363,10 @@ struct is_constructible_string_type
 #endif
 
     static constexpr auto value =
-        is_constructible<laundered_type,
-        typename BasicJsonType::string_t>::value;
+        conjunction <
+        is_constructible<laundered_type, typename BasicJsonType::string_t>,
+        is_detected_exact<typename BasicJsonType::string_t::value_type,
+        value_type_t, laundered_type >>::value;
 };
 
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -3651,8 +3651,10 @@ struct is_constructible_string_type
 #endif
 
     static constexpr auto value =
-        is_constructible<laundered_type,
-        typename BasicJsonType::string_t>::value;
+        conjunction <
+        is_constructible<laundered_type, typename BasicJsonType::string_t>,
+        is_detected_exact<typename BasicJsonType::string_t::value_type,
+        value_type_t, laundered_type >>::value;
 };
 
 template<typename BasicJsonType, typename CompatibleArrayType, typename = void>
@@ -4478,6 +4480,7 @@ template <
     typename BasicJsonType, typename StringType,
     enable_if_t <
         std::is_assignable<StringType&, const typename BasicJsonType::string_t>::value
+        && is_detected_exact<typename BasicJsonType::string_t::value_type, value_type_t, StringType>::value
         && !std::is_same<typename BasicJsonType::string_t, StringType>::value
         && !is_json_ref<StringType>::value, int > = 0 >
 inline void from_json(const BasicJsonType& j, StringType& s)