Move public facing SFINAEs to template declarations

CHANGELOG.md

@@ -10,6 +10,7 @@ HEAD
 * `JsonString` is now stored by copy, unless specified otherwise
 * Replace undocumented `JsonString::Ownership` with `bool`
 * Rename undocumented `JsonString::isLinked()` to `isStatic()`
+* Move public facing SFINAEs to template declarations
 
 > ### BREAKING CHANGES
 >

src/ArduinoJson/Array/JsonArray.hpp

@@ -43,16 +43,18 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
   // Appends a new (empty) element to the array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsonarray/add/
-  template <typename T>
+  template <typename T, detail::enable_if_t<
-  detail::enable_if_t<!detail::is_same<T, JsonVariant>::value, T> add() const {
+                            !detail::is_same<T, JsonVariant>::value, int> = 0>
+  T add() const {
     return add<JsonVariant>().to<T>();
   }
 
   // Appends a new (null) element to the array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsonarray/add/
-  template <typename T>
+  template <typename T, detail::enable_if_t<
-  detail::enable_if_t<detail::is_same<T, JsonVariant>::value, T> add() const {
+                            detail::is_same<T, JsonVariant>::value, int> = 0>
+  JsonVariant add() const {
     return JsonVariant(detail::ArrayData::addElement(data_, resources_),
                        resources_);
   }
@@ -67,7 +69,7 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonarray/add/
   template <typename T,
-            typename = detail::enable_if_t<!detail::is_const<T>::value>>
+            detail::enable_if_t<!detail::is_const<T>::value, int> = 0>
   bool add(T* value) const {
     return detail::ArrayData::addValue(data_, value, resources_);
   }
@@ -115,9 +117,9 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
 
   // Removes the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarray/remove/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-      const TVariant& variant) const {
+  void remove(const TVariant& variant) const {
     if (variant.template is<size_t>())
       remove(variant.template as<size_t>());
   }
@@ -130,19 +132,17 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
 
   // Gets or sets the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarray/subscript/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<detail::is_integral<T>::value,
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
-                      detail::ElementProxy<JsonArray>>
+  detail::ElementProxy<JsonArray> operator[](T index) const {
-  operator[](T index) const {
     return {*this, size_t(index)};
   }
 
   // Gets or sets the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarray/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-                      detail::ElementProxy<JsonArray>>
+  detail::ElementProxy<JsonArray> operator[](const TVariant& variant) const {
-  operator[](const TVariant& variant) const {
     if (variant.template is<size_t>())
       return {*this, variant.template as<size_t>()};
     else

src/ArduinoJson/Array/JsonArrayConst.hpp

@@ -45,9 +45,9 @@ class JsonArrayConst : public detail::VariantOperators<JsonArrayConst> {
 
   // Returns the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarrayconst/subscript/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<detail::is_integral<T>::value, JsonVariantConst>
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
-  operator[](T index) const {
+  JsonVariantConst operator[](T index) const {
     return JsonVariantConst(
         detail::ArrayData::getElement(data_, size_t(index), resources_),
         resources_);
@@ -55,9 +55,9 @@ class JsonArrayConst : public detail::VariantOperators<JsonArrayConst> {
 
   // Returns the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarrayconst/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-  operator[](const TVariant& variant) const {
+  JsonVariantConst operator[](const TVariant& variant) const {
     if (variant.template is<size_t>())
       return operator[](variant.template as<size_t>());
     else

src/ArduinoJson/Array/Utilities.hpp

@@ -11,27 +11,26 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Copies a value to a JsonVariant.
 // This is a degenerated form of copyArray() to stop the recursion.
-template <typename T>
+template <typename T, detail::enable_if_t<!detail::is_array<T>::value, int> = 0>
-inline detail::enable_if_t<!detail::is_array<T>::value, bool> copyArray(
+inline bool copyArray(const T& src, JsonVariant dst) {
-    const T& src, JsonVariant dst) {
   return dst.set(src);
 }
 
 // Copies values from an array to a JsonArray or a JsonVariant.
 // https://arduinojson.org/v7/api/misc/copyarray/
-template <typename T, size_t N, typename TDestination>
+template <typename T, size_t N, typename TDestination,
-inline detail::enable_if_t<
+          detail::enable_if_t<
-    !detail::is_base_of<JsonDocument, TDestination>::value, bool>
+              !detail::is_base_of<JsonDocument, TDestination>::value, int> = 0>
-copyArray(T (&src)[N], const TDestination& dst) {
+inline bool copyArray(T (&src)[N], const TDestination& dst) {
   return copyArray(src, N, dst);
 }
 
 // Copies values from an array to a JsonArray or a JsonVariant.
 // https://arduinojson.org/v7/api/misc/copyarray/
-template <typename T, typename TDestination>
+template <typename T, typename TDestination,
-inline detail::enable_if_t<
+          detail::enable_if_t<
-    !detail::is_base_of<JsonDocument, TDestination>::value, bool>
+              !detail::is_base_of<JsonDocument, TDestination>::value, int> = 0>
-copyArray(const T* src, size_t len, const TDestination& dst) {
+inline bool copyArray(const T* src, size_t len, const TDestination& dst) {
   bool ok = true;
   for (size_t i = 0; i < len; i++) {
     ok &= copyArray(src[i], dst.template add<JsonVariant>());
@@ -62,9 +61,8 @@ inline bool copyArray(const T* src, size_t len, JsonDocument& dst) {
 
 // Copies a value from a JsonVariant.
 // This is a degenerated form of copyArray() to stop the recursion.
-template <typename T>
+template <typename T, detail::enable_if_t<!detail::is_array<T>::value, int> = 0>
-inline detail::enable_if_t<!detail::is_array<T>::value, size_t> copyArray(
+inline size_t copyArray(JsonVariantConst src, T& dst) {
-    JsonVariantConst src, T& dst) {
   dst = src.as<T>();
   return 1;
 }
@@ -102,11 +100,12 @@ inline size_t copyArray(JsonVariantConst src, char (&dst)[N]) {
 
 // Copies values from a JsonDocument to an array.
 // https://arduinojson.org/v7/api/misc/copyarray/
-template <typename TSource, typename T>
+template <
-inline detail::enable_if_t<detail::is_array<T>::value &&
+    typename TSource, typename T,
-                               detail::is_base_of<JsonDocument, TSource>::value,
+    detail::enable_if_t<detail::is_array<T>::value &&
-                           size_t>
+                            detail::is_base_of<JsonDocument, TSource>::value,
-copyArray(const TSource& src, T& dst) {
+                        int> = 0>
+inline size_t copyArray(const TSource& src, T& dst) {
   return copyArray(src.template as<JsonArrayConst>(), dst);
 }
 

src/ArduinoJson/Deserialization/deserialize.hpp

@@ -55,10 +55,11 @@ DeserializationError doDeserialize(TDestination&& dst, TReader reader,
   return err;
 }
 
-template <template <typename> class TDeserializer, typename TDestination,
+template <
-          typename TStream, typename... Args,
+    template <typename> class TDeserializer, typename TDestination,
-          typename = enable_if_t<  // issue #1897
+    typename TStream, typename... Args,
-              !is_integral<typename first_or_void<Args...>::type>::value>>
+    enable_if_t<  // issue #1897
+        !is_integral<typename first_or_void<Args...>::type>::value, int> = 0>
 DeserializationError deserialize(TDestination&& dst, TStream&& input,
                                  Args... args) {
   return doDeserialize<TDeserializer>(
@@ -68,7 +69,7 @@ DeserializationError deserialize(TDestination&& dst, TStream&& input,
 
 template <template <typename> class TDeserializer, typename TDestination,
           typename TChar, typename Size, typename... Args,
-          typename = enable_if_t<is_integral<Size>::value>>
+          enable_if_t<is_integral<Size>::value, int> = 0>
 DeserializationError deserialize(TDestination&& dst, TChar* input,
                                  Size inputSize, Args... args) {
   return doDeserialize<TDeserializer>(dst, makeReader(input, size_t(inputSize)),

src/ArduinoJson/Document/JsonDocument.hpp

@@ -36,14 +36,15 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   }
 
   // Construct from variant, array, or object
-  template <typename T>
+  template <typename T,
-  JsonDocument(
+            detail::enable_if_t<detail::IsVariant<T>::value ||
-      const T& src, Allocator* alloc = detail::DefaultAllocator::instance(),
+                                    detail::is_same<T, JsonArray>::value ||
-      detail::enable_if_t<detail::IsVariant<T>::value ||
+                                    detail::is_same<T, JsonArrayConst>::value ||
-                          detail::is_same<T, JsonArray>::value ||
+                                    detail::is_same<T, JsonObject>::value ||
-                          detail::is_same<T, JsonArrayConst>::value ||
+                                    detail::is_same<T, JsonObjectConst>::value,
-                          detail::is_same<T, JsonObject>::value ||
+                                int> = 0>
-                          detail::is_same<T, JsonObjectConst>::value>* = 0)
+  JsonDocument(const T& src,
+               Allocator* alloc = detail::DefaultAllocator::instance())
       : JsonDocument(alloc) {
     set(src);
   }
@@ -136,16 +137,17 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Replaces the root with the specified value.
   // https://arduinojson.org/v7/api/jsondocument/set/
-  template <typename T>
+  template <
-  detail::enable_if_t<!detail::is_base_of<JsonDocument, T>::value, bool> set(
+      typename T,
-      const T& src) {
+      detail::enable_if_t<!detail::is_base_of<JsonDocument, T>::value, int> = 0>
+  bool set(const T& src) {
     return to<JsonVariant>().set(src);
   }
 
   // Replaces the root with the specified value.
   // https://arduinojson.org/v7/api/jsondocument/set/
   template <typename TChar,
-            typename = detail::enable_if_t<!detail::is_const<TChar>::value>>
+            detail::enable_if_t<!detail::is_const<TChar>::value, int> = 0>
   bool set(TChar* src) {
     return to<JsonVariant>().set(src);
   }
@@ -168,68 +170,67 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsondocument/containskey/
-  template <typename TString>
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use doc[key].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TString>::value, bool> containsKey(
+  bool containsKey(const TString& key) const {
-      const TString& key) const {
     return data_.getMember(detail::adaptString(key), &resources_) != 0;
   }
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsondocument/containskey/
-  template <typename TVariant>
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use doc[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
+  bool containsKey(const TVariant& key) const {
-      const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 
   // Gets or sets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-      detail::IsString<TString>::value,
+  detail::MemberProxy<JsonDocument&, detail::AdaptedString<TString>> operator[](
-      detail::MemberProxy<JsonDocument&, detail::AdaptedString<TString>>>
+      const TString& key) {
-  operator[](const TString& key) {
     return {*this, detail::adaptString(key)};
   }
 
   // Gets or sets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
+                                    !detail::is_const<TChar>::value,
-      detail::MemberProxy<JsonDocument&, detail::AdaptedString<TChar*>>>
+                                int> = 0>
-  operator[](TChar* key) {
+  detail::MemberProxy<JsonDocument&, detail::AdaptedString<TChar*>> operator[](
+      TChar* key) {
     return {*this, detail::adaptString(key)};
   }
 
   // Gets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-  operator[](const TString& key) const {
+  JsonVariantConst operator[](const TString& key) const {
     return JsonVariantConst(
         data_.getMember(detail::adaptString(key), &resources_), &resources_);
   }
 
   // Gets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
+                                    !detail::is_const<TChar>::value,
-                      JsonVariantConst>
+                                int> = 0>
-  operator[](TChar* key) const {
+  JsonVariantConst operator[](TChar* key) const {
     return JsonVariantConst(
         data_.getMember(detail::adaptString(key), &resources_), &resources_);
   }
 
   // Gets or sets a root array's element.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<detail::is_integral<T>::value,
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
-                      detail::ElementProxy<JsonDocument&>>
+  detail::ElementProxy<JsonDocument&> operator[](T index) {
-  operator[](T index) {
     return {*this, size_t(index)};
   }
 
@@ -241,9 +242,9 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Gets or sets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-  operator[](const TVariant& key) const {
+  JsonVariantConst operator[](const TVariant& key) const {
     if (key.template is<JsonString>())
       return operator[](key.template as<JsonString>());
     if (key.template is<size_t>())
@@ -254,16 +255,18 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   // Appends a new (empty) element to the root array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsondocument/add/
-  template <typename T>
+  template <typename T, detail::enable_if_t<
-  detail::enable_if_t<!detail::is_same<T, JsonVariant>::value, T> add() {
+                            !detail::is_same<T, JsonVariant>::value, int> = 0>
+  T add() {
     return add<JsonVariant>().to<T>();
   }
 
   // Appends a new (null) element to the root array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsondocument/add/
-  template <typename T>
+  template <typename T, detail::enable_if_t<
-  detail::enable_if_t<detail::is_same<T, JsonVariant>::value, T> add() {
+                            detail::is_same<T, JsonVariant>::value, int> = 0>
+  JsonVariant add() {
     return JsonVariant(data_.addElement(&resources_), &resources_);
   }
 
@@ -277,43 +280,45 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   // Appends a value to the root array.
   // https://arduinojson.org/v7/api/jsondocument/add/
   template <typename TChar,
-            typename = detail::enable_if_t<!detail::is_const<TChar>::value>>
+            detail::enable_if_t<!detail::is_const<TChar>::value, int> = 0>
   bool add(TChar* value) {
     return data_.addValue(value, &resources_);
   }
 
   // Removes an element of the root array.
   // https://arduinojson.org/v7/api/jsondocument/remove/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<detail::is_integral<T>::value> remove(T index) {
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
+  void remove(T index) {
     detail::VariantData::removeElement(getData(), size_t(index),
                                        getResourceManager());
   }
 
   // Removes a member of the root object.
   // https://arduinojson.org/v7/api/jsondocument/remove/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-                      !detail::is_const<TChar>::value>
+                                    !detail::is_const<TChar>::value,
-  remove(TChar* key) {
+                                int> = 0>
+  void remove(TChar* key) {
     detail::VariantData::removeMember(getData(), detail::adaptString(key),
                                       getResourceManager());
   }
 
   // Removes a member of the root object.
   // https://arduinojson.org/v7/api/jsondocument/remove/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<detail::IsString<TString>::value> remove(
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-      const TString& key) {
+  void remove(const TString& key) {
     detail::VariantData::removeMember(getData(), detail::adaptString(key),
                                       getResourceManager());
   }
 
   // Removes a member of the root object or an element of the root array.
   // https://arduinojson.org/v7/api/jsondocument/remove/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-      const TVariant& key) {
+  void remove(const TVariant& key) {
     if (key.template is<const char*>())
       remove(key.template as<const char*>());
     if (key.template is<size_t>())

src/ArduinoJson/Json/JsonDeserializer.hpp

@@ -697,10 +697,11 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Parses a JSON input, filters, and puts the result in a JsonDocument.
 // https://arduinojson.org/v7/api/json/deserializejson/
-template <typename TDestination, typename... Args>
+template <typename TDestination, typename... Args,
-detail::enable_if_t<detail::is_deserialize_destination<TDestination>::value,
+          detail::enable_if_t<
-                    DeserializationError>
+              detail::is_deserialize_destination<TDestination>::value, int> = 0>
-deserializeJson(TDestination&& dst, Args&&... args) {
+inline DeserializationError deserializeJson(TDestination&& dst,
+                                            Args&&... args) {
   using namespace detail;
   return deserialize<JsonDeserializer>(detail::forward<TDestination>(dst),
                                        detail::forward<Args>(args)...);
@@ -708,10 +709,11 @@ deserializeJson(TDestination&& dst, Args&&... args) {
 
 // Parses a JSON input, filters, and puts the result in a JsonDocument.
 // https://arduinojson.org/v7/api/json/deserializejson/
-template <typename TDestination, typename TChar, typename... Args>
+template <typename TDestination, typename TChar, typename... Args,
-detail::enable_if_t<detail::is_deserialize_destination<TDestination>::value,
+          detail::enable_if_t<
-                    DeserializationError>
+              detail::is_deserialize_destination<TDestination>::value, int> = 0>
-deserializeJson(TDestination&& dst, TChar* input, Args&&... args) {
+inline DeserializationError deserializeJson(TDestination&& dst, TChar* input,
+                                            Args&&... args) {
   using namespace detail;
   return deserialize<JsonDeserializer>(detail::forward<TDestination>(dst),
                                        input, detail::forward<Args>(args)...);

src/ArduinoJson/Json/JsonSerializer.hpp

@@ -129,9 +129,10 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Produces a minified JSON document.
 // https://arduinojson.org/v7/api/json/serializejson/
-template <typename TDestination>
+template <
-detail::enable_if_t<!detail::is_pointer<TDestination>::value, size_t>
+    typename TDestination,
-serializeJson(JsonVariantConst source, TDestination& destination) {
+    detail::enable_if_t<!detail::is_pointer<TDestination>::value, int> = 0>
+size_t serializeJson(JsonVariantConst source, TDestination& destination) {
   using namespace detail;
   return serialize<JsonSerializer>(source, destination);
 }
@@ -152,10 +153,10 @@ inline size_t measureJson(JsonVariantConst source) {
 }
 
 #if ARDUINOJSON_ENABLE_STD_STREAM
-template <typename T>
+template <typename T,
-inline detail::enable_if_t<detail::is_convertible<T, JsonVariantConst>::value,
+          detail::enable_if_t<
-                           std::ostream&>
+              detail::is_convertible<T, JsonVariantConst>::value, int> = 0>
-operator<<(std::ostream& os, const T& source) {
+inline std::ostream& operator<<(std::ostream& os, const T& source) {
   serializeJson(source, os);
   return os;
 }

src/ArduinoJson/Json/PrettyJsonSerializer.hpp

@@ -83,9 +83,11 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Produces JsonDocument to create a prettified JSON document.
 // https://arduinojson.org/v7/api/json/serializejsonpretty/
-template <typename TDestination>
+template <
-detail::enable_if_t<!detail::is_pointer<TDestination>::value, size_t>
+    typename TDestination,
-serializeJsonPretty(JsonVariantConst source, TDestination& destination) {
+    detail::enable_if_t<!detail::is_pointer<TDestination>::value, int> = 0>
+inline size_t serializeJsonPretty(JsonVariantConst source,
+                                  TDestination& destination) {
   using namespace ArduinoJson::detail;
   return serialize<PrettyJsonSerializer>(source, destination);
 }

src/ArduinoJson/MsgPack/MsgPackDeserializer.hpp

@@ -464,10 +464,11 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Parses a MessagePack input and puts the result in a JsonDocument.
 // https://arduinojson.org/v7/api/msgpack/deserializemsgpack/
-template <typename TDestination, typename... Args>
+template <typename TDestination, typename... Args,
-detail::enable_if_t<detail::is_deserialize_destination<TDestination>::value,
+          detail::enable_if_t<
-                    DeserializationError>
+              detail::is_deserialize_destination<TDestination>::value, int> = 0>
-deserializeMsgPack(TDestination&& dst, Args&&... args) {
+inline DeserializationError deserializeMsgPack(TDestination&& dst,
+                                               Args&&... args) {
   using namespace detail;
   return deserialize<MsgPackDeserializer>(detail::forward<TDestination>(dst),
                                           detail::forward<Args>(args)...);
@@ -475,10 +476,11 @@ deserializeMsgPack(TDestination&& dst, Args&&... args) {
 
 // Parses a MessagePack input and puts the result in a JsonDocument.
 // https://arduinojson.org/v7/api/msgpack/deserializemsgpack/
-template <typename TDestination, typename TChar, typename... Args>
+template <typename TDestination, typename TChar, typename... Args,
-detail::enable_if_t<detail::is_deserialize_destination<TDestination>::value,
+          detail::enable_if_t<
-                    DeserializationError>
+              detail::is_deserialize_destination<TDestination>::value, int> = 0>
-deserializeMsgPack(TDestination&& dst, TChar* input, Args&&... args) {
+inline DeserializationError deserializeMsgPack(TDestination&& dst, TChar* input,
+                                               Args&&... args) {
   using namespace detail;
   return deserialize<MsgPackDeserializer>(detail::forward<TDestination>(dst),
                                           input,

src/ArduinoJson/MsgPack/MsgPackSerializer.hpp

@@ -218,9 +218,10 @@ ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 // Produces a MessagePack document.
 // https://arduinojson.org/v7/api/msgpack/serializemsgpack/
-template <typename TDestination>
+template <
-detail::enable_if_t<!detail::is_pointer<TDestination>::value, size_t>
+    typename TDestination,
-serializeMsgPack(JsonVariantConst source, TDestination& output) {
+    detail::enable_if_t<!detail::is_pointer<TDestination>::value, int> = 0>
+inline size_t serializeMsgPack(JsonVariantConst source, TDestination& output) {
   using namespace ArduinoJson::detail;
   return serialize<MsgPackSerializer>(source, output);
 }

src/ArduinoJson/Object/JsonObject.hpp

@@ -101,31 +101,30 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
 
   // Gets or sets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobject/subscript/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-      detail::IsString<TString>::value,
+  detail::MemberProxy<JsonObject, detail::AdaptedString<TString>> operator[](
-      detail::MemberProxy<JsonObject, detail::AdaptedString<TString>>>
+      const TString& key) const {
-  operator[](const TString& key) const {
     return {*this, detail::adaptString(key)};
   }
 
   // Gets or sets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobject/subscript/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
+                                    !detail::is_const<TChar>::value,
-      detail::MemberProxy<JsonObject, detail::AdaptedString<TChar*>>>
+                                int> = 0>
-  operator[](TChar* key) const {
+  detail::MemberProxy<JsonObject, detail::AdaptedString<TChar*>> operator[](
+      TChar* key) const {
     return {*this, detail::adaptString(key)};
   }
 
   // Gets or sets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobject/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-      detail::IsVariant<TVariant>::value,
+  detail::MemberProxy<JsonObject, detail::AdaptedString<JsonString>> operator[](
-      detail::MemberProxy<JsonObject, detail::AdaptedString<JsonString>>>
+      const TVariant& key) const {
-  operator[](const TVariant& key) const {
     return {*this, detail::adaptString(key.template as<JsonString>())};
   }
 
@@ -137,18 +136,18 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
 
   // Removes the member with the specified key.
   // https://arduinojson.org/v7/api/jsonobject/remove/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<detail::IsString<TString>::value> remove(
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-      const TString& key) const {
+  void remove(const TString& key) const {
     detail::ObjectData::removeMember(data_, detail::adaptString(key),
                                      resources_);
   }
 
   // Removes the member with the specified key.
   // https://arduinojson.org/v7/api/jsonobject/remove/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-      const TVariant& key) const {
+  void remove(const TVariant& key) const {
     if (key.template is<const char*>())
       remove(key.template as<const char*>());
   }
@@ -163,31 +162,32 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonobject/containskey/
-  template <typename TString>
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TString>::value, bool> containsKey(
+  bool containsKey(const TString& key) const {
-      const TString& key) const {
     return detail::ObjectData::getMember(data_, detail::adaptString(key),
                                          resources_) != 0;
   }
 
   // DEPRECATED: use obj["key"].is<T>() instead
   // https://arduinojson.org/v7/api/jsonobject/containskey/
-  template <typename TChar>
+  template <typename TChar,
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                    !detail::is_const<TChar>::value,
+                                int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+  bool containsKey(TChar* key) const {
-                          !detail::is_const<TChar>::value,
-                      bool> containsKey(TChar* key) const {
     return detail::ObjectData::getMember(data_, detail::adaptString(key),
                                          resources_) != 0;
   }
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonobject/containskey/
-  template <typename TVariant>
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
+  bool containsKey(const TVariant& key) const {
-      const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 

src/ArduinoJson/Object/JsonObjectConst.hpp

@@ -70,10 +70,10 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonobjectconst/containskey/
-  template <typename TString>
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TString>::value, bool> containsKey(
+  bool containsKey(const TString& key) const {
-      const TString& key) const {
     return detail::ObjectData::getMember(data_, detail::adaptString(key),
                                          resources_) != 0;
   }
@@ -89,18 +89,18 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonobjectconst/containskey/
-  template <typename TVariant>
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
+  bool containsKey(const TVariant& key) const {
-      const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 
   // Gets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobjectconst/subscript/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-  operator[](const TString& key) const {
+  JsonVariantConst operator[](const TString& key) const {
     return JsonVariantConst(detail::ObjectData::getMember(
                                 data_, detail::adaptString(key), resources_),
                             resources_);
@@ -108,11 +108,11 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
 
   // Gets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobjectconst/subscript/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
+                                    !detail::is_const<TChar>::value,
-                      JsonVariantConst>
+                                int> = 0>
-  operator[](TChar* key) const {
+  JsonVariantConst operator[](TChar* key) const {
     return JsonVariantConst(detail::ObjectData::getMember(
                                 data_, detail::adaptString(key), resources_),
                             resources_);
@@ -120,9 +120,9 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
 
   // Gets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobjectconst/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-  operator[](const TVariant& key) const {
+  JsonVariantConst operator[](const TVariant& key) const {
     if (key.template is<JsonString>())
       return operator[](key.template as<JsonString>());
     else

src/ArduinoJson/Object/MemberProxy.hpp

@@ -39,7 +39,7 @@ class MemberProxy
     return *this;
   }
 
-  template <typename T, typename = enable_if_t<!is_const<T>::value>>
+  template <typename T, enable_if_t<!is_const<T>::value, int> = 0>
   MemberProxy& operator=(T* src) {
     this->set(src);
     return *this;

src/ArduinoJson/Strings/JsonString.hpp

@@ -24,9 +24,10 @@ class JsonString {
   JsonString(const char* data, bool isStatic = false)
       : str_(data, data ? ::strlen(data) : 0, isStatic) {}
 
-  template <typename TSize, typename = detail::enable_if_t<
+  template <typename TSize,
-                                detail::is_integral<TSize>::value &&
+            detail::enable_if_t<detail::is_integral<TSize>::value &&
-                                !detail::is_same<TSize, bool>::value>>
+                                    !detail::is_same<TSize, bool>::value,
+                                int> = 0>
   JsonString(const char* data, TSize sz, bool isStatic = false)
       : str_(data, size_t(sz), isStatic) {}
 

src/ArduinoJson/Strings/StringAdapter.hpp

@@ -34,7 +34,7 @@ AdaptedString<TString> adaptString(TString&& s) {
   return StringAdapterFor<TString>::adapt(detail::forward<TString>(s));
 }
 
-template <typename TChar, typename = enable_if_t<!is_const<TChar>::value>>
+template <typename TChar, enable_if_t<!is_const<TChar>::value, int> = 0>
 AdaptedString<TChar*> adaptString(TChar* p) {
   return StringAdapter<TChar*>::adapt(p);
 }

src/ArduinoJson/Variant/JsonVariantConst.hpp

@@ -68,27 +68,29 @@ class JsonVariantConst : public detail::VariantTag,
   // Casts the value to the specified type.
   // https://arduinojson.org/v7/api/jsonvariantconst/as/
   template <typename T,
-            detail::enable_if_t<ConversionSupported<T>::value, bool> = true>
+            detail::enable_if_t<ConversionSupported<T>::value, int> = 0>
   T as() const {
     return Converter<T>::fromJson(*this);
   }
 
   // Invalid conversion. Will not compile.
   template <typename T,
-            detail::enable_if_t<!ConversionSupported<T>::value, bool> = true>
+            detail::enable_if_t<!ConversionSupported<T>::value, int> = 0>
   detail::InvalidConversion<JsonVariantConst, T> as() const;
 
   // Returns true if the value is of the specified type.
   // https://arduinojson.org/v7/api/jsonvariantconst/is/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<ConversionSupported<T>::value, bool> is() const {
+            detail::enable_if_t<ConversionSupported<T>::value, int> = 0>
+  bool is() const {
     return Converter<T>::checkJson(*this);
   }
 
   // Always returns false for the unsupported types.
   // https://arduinojson.org/v7/api/jsonvariantconst/is/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<!ConversionSupported<T>::value, bool> is() const {
+            detail::enable_if_t<!ConversionSupported<T>::value, int> = 0>
+  bool is() const {
     return false;
   }
 
@@ -99,9 +101,9 @@ class JsonVariantConst : public detail::VariantTag,
 
   // Gets array's element at specified index.
   // https://arduinojson.org/v7/api/jsonvariantconst/subscript/
-  template <typename T>
+  template <typename T,
-  detail::enable_if_t<detail::is_integral<T>::value, JsonVariantConst>
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
-  operator[](T index) const {
+  JsonVariantConst operator[](T index) const {
     return JsonVariantConst(
         detail::VariantData::getElement(data_, size_t(index), resources_),
         resources_);
@@ -109,9 +111,9 @@ class JsonVariantConst : public detail::VariantTag,
 
   // Gets object's member with specified key.
   // https://arduinojson.org/v7/api/jsonvariantconst/subscript/
-  template <typename TString>
+  template <typename TString,
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
-  operator[](const TString& key) const {
+  JsonVariantConst operator[](const TString& key) const {
     return JsonVariantConst(detail::VariantData::getMember(
                                 data_, detail::adaptString(key), resources_),
                             resources_);
@@ -119,11 +121,11 @@ class JsonVariantConst : public detail::VariantTag,
 
   // Gets object's member with specified key.
   // https://arduinojson.org/v7/api/jsonvariantconst/subscript/
-  template <typename TChar>
+  template <typename TChar,
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
+                                    !detail::is_const<TChar>::value,
-                      JsonVariantConst>
+                                int> = 0>
-  operator[](TChar* key) const {
+  JsonVariantConst operator[](TChar* key) const {
     return JsonVariantConst(detail::VariantData::getMember(
                                 data_, detail::adaptString(key), resources_),
                             resources_);
@@ -132,9 +134,9 @@ class JsonVariantConst : public detail::VariantTag,
   // Gets object's member with specified key or the array's element at the
   // specified index.
   // https://arduinojson.org/v7/api/jsonvariantconst/subscript/
-  template <typename TVariant>
+  template <typename TVariant,
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
-  operator[](const TVariant& key) const {
+  JsonVariantConst operator[](const TVariant& key) const {
     if (key.template is<size_t>())
       return operator[](key.template as<size_t>());
     else
@@ -143,31 +145,32 @@ class JsonVariantConst : public detail::VariantTag,
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariantconst/containskey/
-  template <typename TString>
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use var[key].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TString>::value, bool> containsKey(
+  bool containsKey(const TString& key) const {
-      const TString& key) const {
     return detail::VariantData::getMember(getData(), detail::adaptString(key),
                                           resources_) != 0;
   }
 
   // DEPRECATED: use obj["key"].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariantconst/containskey/
-  template <typename TChar>
+  template <typename TChar,
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                    !detail::is_const<TChar>::value,
+                                int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
+  bool containsKey(TChar* key) const {
-                          !detail::is_const<TChar>::value,
-                      bool> containsKey(TChar* key) const {
     return detail::VariantData::getMember(getData(), detail::adaptString(key),
                                           resources_) != 0;
   }
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariantconst/containskey/
-  template <typename TVariant>
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use var[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
+  bool containsKey(const TVariant& key) const {
-      const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 

src/ArduinoJson/Variant/VariantOperators.hpp

@@ -30,9 +30,9 @@ struct VariantOperators : VariantOperatorTag {
   // int operator|(JsonVariant, int)
   // float operator|(JsonVariant, float)
   // bool operator|(JsonVariant, bool)
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!IsVariant<T>::value && !is_array<T>::value, T> operator|(
+            enable_if_t<!IsVariant<T>::value && !is_array<T>::value, int> = 0>
-      const TVariant& variant, const T& defaultValue) {
+  friend T operator|(const TVariant& variant, const T& defaultValue) {
     if (variant.template is<T>())
       return variant.template as<T>();
     else
@@ -73,9 +73,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator==(const TVariant& lhs, T* rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_EQUAL;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-  operator==(const TVariant& lhs, const T& rhs) {
+  friend bool operator==(const TVariant& lhs, const T& rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_EQUAL;
   }
 
@@ -94,9 +94,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator!=(const TVariant& lhs, T* rhs) {
     return compare(lhs, rhs) != COMPARE_RESULT_EQUAL;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-  operator!=(TVariant lhs, const T& rhs) {
+  friend bool operator!=(TVariant lhs, const T& rhs) {
     return compare(lhs, rhs) != COMPARE_RESULT_EQUAL;
   }
 
@@ -115,9 +115,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator<(const TVariant& lhs, T* rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_LESS;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool> operator<(
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-      TVariant lhs, const T& rhs) {
+  friend bool operator<(TVariant lhs, const T& rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_LESS;
   }
 
@@ -136,9 +136,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator<=(const TVariant& lhs, T* rhs) {
     return (compare(lhs, rhs) & COMPARE_RESULT_LESS_OR_EQUAL) != 0;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-  operator<=(TVariant lhs, const T& rhs) {
+  friend bool operator<=(TVariant lhs, const T& rhs) {
     return (compare(lhs, rhs) & COMPARE_RESULT_LESS_OR_EQUAL) != 0;
   }
 
@@ -157,9 +157,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator>(const TVariant& lhs, T* rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_GREATER;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool> operator>(
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-      TVariant lhs, const T& rhs) {
+  friend bool operator>(TVariant lhs, const T& rhs) {
     return compare(lhs, rhs) == COMPARE_RESULT_GREATER;
   }
 
@@ -178,9 +178,9 @@ struct VariantOperators : VariantOperatorTag {
   friend bool operator>=(const TVariant& lhs, T* rhs) {
     return (compare(lhs, rhs) & COMPARE_RESULT_GREATER_OR_EQUAL) != 0;
   }
-  template <typename T>
+  template <typename T,
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
+            enable_if_t<!is_base_of<VariantOperatorTag, T>::value, int> = 0>
-  operator>=(const TVariant& lhs, const T& rhs) {
+  friend bool operator>=(const TVariant& lhs, const T& rhs) {
     return (compare(lhs, rhs) & COMPARE_RESULT_GREATER_OR_EQUAL) != 0;
   }
 };

src/ArduinoJson/Variant/VariantRefBase.hpp

@@ -48,25 +48,25 @@ class VariantRefBase : public VariantTag {
   template <typename T>
   T as() const;
 
-  template <typename T, typename = enable_if_t<!is_same<T, TDerived>::value>>
+  template <typename T, enable_if_t<!is_same<T, TDerived>::value, int> = 0>
   operator T() const {
     return as<T>();
   }
 
   // Sets the value to an empty array.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
+  template <typename T, enable_if_t<is_same<T, JsonArray>::value, int> = 0>
-  enable_if_t<is_same<T, JsonArray>::value, JsonArray> to() const;
+  JsonArray to() const;
 
   // Sets the value to an empty object.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
+  template <typename T, enable_if_t<is_same<T, JsonObject>::value, int> = 0>
-  enable_if_t<is_same<T, JsonObject>::value, JsonObject> to() const;
+  JsonObject to() const;
 
   // Sets the value to null.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
+  template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int> = 0>
-  enable_if_t<is_same<T, JsonVariant>::value, JsonVariant> to() const;
+  JsonVariant to() const;
 
   // Returns true if the value is of the specified type.
   // https://arduinojson.org/v7/api/jsonvariant/is/
@@ -85,7 +85,7 @@ class VariantRefBase : public VariantTag {
   // Copies the specified value.
   // https://arduinojson.org/v7/api/jsonvariant/set/
   template <typename T,
-            typename = detail::enable_if_t<!detail::is_const<T>::value>>
+            detail::enable_if_t<!detail::is_const<T>::value, int> = 0>
   bool set(T* value) const {
     return doSet<Converter<T*>>(value);
   }
@@ -105,16 +105,16 @@ class VariantRefBase : public VariantTag {
   // Appends a new (empty) element to the array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsonvariant/add/
-  template <typename T>
+  template <typename T, enable_if_t<!is_same<T, JsonVariant>::value, int> = 0>
-  enable_if_t<!is_same<T, JsonVariant>::value, T> add() const {
+  T add() const {
     return add<JsonVariant>().template to<T>();
   }
 
   // Appends a new (null) element to the array.
   // Returns a reference to the new element.
   // https://arduinojson.org/v7/api/jsonvariant/add/
-  template <typename T>
+  template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int> = 0>
-  enable_if_t<is_same<T, JsonVariant>::value, T> add() const;
+  T add() const;
 
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonvariant/add/
@@ -126,7 +126,7 @@ class VariantRefBase : public VariantTag {
 
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonvariant/add/
-  template <typename T, typename = enable_if_t<!is_const<T>::value>>
+  template <typename T, enable_if_t<!is_const<T>::value, int> = 0>
   bool add(T* value) const {
     return detail::VariantData::addValue(getOrCreateData(), value,
                                          getResourceManager());
@@ -140,24 +140,24 @@ class VariantRefBase : public VariantTag {
 
   // Removes a member of the object.
   // https://arduinojson.org/v7/api/jsonvariant/remove/
-  template <typename TChar>
+  template <typename TChar, enable_if_t<IsString<TChar*>::value, int> = 0>
-  enable_if_t<IsString<TChar*>::value> remove(TChar* key) const {
+  void remove(TChar* key) const {
     VariantData::removeMember(getData(), adaptString(key),
                               getResourceManager());
   }
 
   // Removes a member of the object.
   // https://arduinojson.org/v7/api/jsonvariant/remove/
-  template <typename TString>
+  template <typename TString, enable_if_t<IsString<TString>::value, int> = 0>
-  enable_if_t<IsString<TString>::value> remove(const TString& key) const {
+  void remove(const TString& key) const {
     VariantData::removeMember(getData(), adaptString(key),
                               getResourceManager());
   }
 
   // Removes a member of the object or an element of the array.
   // https://arduinojson.org/v7/api/jsonvariant/remove/
-  template <typename TVariant>
+  template <typename TVariant, enable_if_t<IsVariant<TVariant>::value, int> = 0>
-  enable_if_t<IsVariant<TVariant>::value> remove(const TVariant& key) const {
+  void remove(const TVariant& key) const {
     if (key.template is<size_t>())
       remove(key.template as<size_t>());
     else
@@ -170,43 +170,40 @@ class VariantRefBase : public VariantTag {
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariant/containskey/
-  template <typename TString>
+  template <typename TString, enable_if_t<IsString<TString>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  enable_if_t<IsString<TString>::value, bool> containsKey(
+  bool containsKey(const TString& key) const;
-      const TString& key) const;
 
   // DEPRECATED: use obj["key"].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariant/containskey/
-  template <typename TChar>
+  template <typename TChar, enable_if_t<IsString<TChar*>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  enable_if_t<IsString<TChar*>::value, bool> containsKey(TChar* key) const;
+  bool containsKey(TChar* key) const;
 
   // DEPRECATED: use obj[key].is<T>() instead
   // https://arduinojson.org/v7/api/jsonvariant/containskey/
-  template <typename TVariant>
+  template <typename TVariant, enable_if_t<IsVariant<TVariant>::value, int> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  enable_if_t<IsVariant<TVariant>::value, bool> containsKey(
+  bool containsKey(const TVariant& key) const;
-      const TVariant& key) const;
 
   // Gets or sets an object member.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
-  template <typename TString>
+  template <typename TString, enable_if_t<IsString<TString>::value, int> = 0>
-  FORCE_INLINE enable_if_t<IsString<TString>::value,
+  FORCE_INLINE MemberProxy<TDerived, AdaptedString<TString>> operator[](
-                           MemberProxy<TDerived, AdaptedString<TString>>>
+      const TString& key) const;
-  operator[](const TString& key) const;
 
   // Gets or sets an object member.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
-  template <typename TChar>
+  template <
-  FORCE_INLINE enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
+      typename TChar,
-                           MemberProxy<TDerived, AdaptedString<TChar*>>>
+      enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value, int> = 0>
-  operator[](TChar* key) const;
+  FORCE_INLINE MemberProxy<TDerived, AdaptedString<TChar*>> operator[](
+      TChar* key) const;
 
   // Gets an object member or an array element.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
-  template <typename TVariant>
+  template <typename TVariant, enable_if_t<IsVariant<TVariant>::value, int> = 0>
-  enable_if_t<IsVariant<TVariant>::value, JsonVariantConst> operator[](
+  JsonVariantConst operator[](const TVariant& key) const {
-      const TVariant& key) const {
     if (key.template is<size_t>())
       return operator[](key.template as<size_t>());
     else

src/ArduinoJson/Variant/VariantRefBaseImpl.hpp

@@ -67,34 +67,30 @@ inline void convertToJson(const VariantRefBase<TDerived>& src,
 }
 
 template <typename TDerived>
-template <typename T>
+template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int>>
-inline enable_if_t<is_same<T, JsonVariant>::value, T>
+inline T VariantRefBase<TDerived>::add() const {
-VariantRefBase<TDerived>::add() const {
   return JsonVariant(
       detail::VariantData::addElement(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename TString>
+template <typename TString, enable_if_t<IsString<TString>::value, int>>
-inline enable_if_t<IsString<TString>::value, bool>
+inline bool VariantRefBase<TDerived>::containsKey(const TString& key) const {
-VariantRefBase<TDerived>::containsKey(const TString& key) const {
   return VariantData::getMember(getData(), adaptString(key),
                                 getResourceManager()) != 0;
 }
 
 template <typename TDerived>
-template <typename TChar>
+template <typename TChar, enable_if_t<IsString<TChar*>::value, int>>
-inline enable_if_t<IsString<TChar*>::value, bool>
+inline bool VariantRefBase<TDerived>::containsKey(TChar* key) const {
-VariantRefBase<TDerived>::containsKey(TChar* key) const {
   return VariantData::getMember(getData(), adaptString(key),
                                 getResourceManager()) != 0;
 }
 
 template <typename TDerived>
-template <typename TVariant>
+template <typename TVariant, enable_if_t<IsVariant<TVariant>::value, int>>
-inline enable_if_t<IsVariant<TVariant>::value, bool>
+inline bool VariantRefBase<TDerived>::containsKey(const TVariant& key) const {
-VariantRefBase<TDerived>::containsKey(const TVariant& key) const {
   return containsKey(key.template as<const char*>());
 }
 
@@ -123,17 +119,16 @@ inline ElementProxy<TDerived> VariantRefBase<TDerived>::operator[](
 }
 
 template <typename TDerived>
-template <typename TChar>
+template <typename TChar,
-inline enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
+          enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value, int>>
-                   MemberProxy<TDerived, AdaptedString<TChar*>>>
+inline MemberProxy<TDerived, AdaptedString<TChar*>>
 VariantRefBase<TDerived>::operator[](TChar* key) const {
   return {derived(), adaptString(key)};
 }
 
 template <typename TDerived>
-template <typename TString>
+template <typename TString, enable_if_t<IsString<TString>::value, int>>
-inline enable_if_t<IsString<TString>::value,
+inline MemberProxy<TDerived, AdaptedString<TString>>
-                   MemberProxy<TDerived, AdaptedString<TString>>>
 VariantRefBase<TDerived>::operator[](const TString& key) const {
   return {derived(), adaptString(key)};
 }
@@ -153,27 +148,24 @@ inline bool VariantRefBase<TDerived>::doSet(const T& value, true_type) const {
 }
 
 template <typename TDerived>
-template <typename T>
+template <typename T, enable_if_t<is_same<T, JsonArray>::value, int>>
-inline enable_if_t<is_same<T, JsonArray>::value, JsonArray>
+inline JsonArray VariantRefBase<TDerived>::to() const {
-VariantRefBase<TDerived>::to() const {
   return JsonArray(
       VariantData::toArray(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename T>
+template <typename T, enable_if_t<is_same<T, JsonObject>::value, int>>
-enable_if_t<is_same<T, JsonObject>::value, JsonObject>
+JsonObject VariantRefBase<TDerived>::to() const {
-VariantRefBase<TDerived>::to() const {
   return JsonObject(
       VariantData::toObject(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename T>
+template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int>>
-enable_if_t<is_same<T, JsonVariant>::value, JsonVariant>
+JsonVariant VariantRefBase<TDerived>::to() const {
-VariantRefBase<TDerived>::to() const {
   auto data = getOrCreateData();
   auto resources = getResourceManager();
   detail::VariantData::clear(data, resources);