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>
-  detail::enable_if_t<!detail::is_same<T, JsonVariant>::value, T> add() const {
+  template <typename T, detail::enable_if_t<
+                            !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>
-  detail::enable_if_t<detail::is_same<T, JsonVariant>::value, T> add() const {
+  template <typename T, detail::enable_if_t<
+                            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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
-      const TVariant& variant) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
+  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>
-  detail::enable_if_t<detail::is_integral<T>::value,
-                      detail::ElementProxy<JsonArray>>
-  operator[](T index) const {
+  template <typename T,
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
+  detail::ElementProxy<JsonArray> 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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value,
-                      detail::ElementProxy<JsonArray>>
-  operator[](const TVariant& variant) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
+  detail::ElementProxy<JsonArray> operator[](const TVariant& variant) const {
     if (variant.template is<size_t>())
       return {*this, variant.template as<size_t>()};
     else

src/ArduinoJson/Array/JsonArrayConst.hpp

@@ -45,19 +45,19 @@ class JsonArrayConst : public detail::VariantOperators<JsonArrayConst> {
 
   // Returns the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarrayconst/subscript/
-  template <typename T>
-  detail::enable_if_t<detail::is_integral<T>::value, JsonVariantConst>
-  operator[](T index) const {
+  template <typename T,
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
+  JsonVariantConst operator[](T index) const {
     return JsonVariantConst(
         detail::ArrayData::getElement(data_, size_t(index), resources_),
         resources_);
   }
 
   // Returns the element at the specified index.
   // https://arduinojson.org/v7/api/jsonarrayconst/subscript/
-  template <typename TVariant>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
-  operator[](const TVariant& variant) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, int> = 0>
+  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>
-inline detail::enable_if_t<!detail::is_array<T>::value, bool> copyArray(
-    const T& src, JsonVariant dst) {
+template <typename T, detail::enable_if_t<!detail::is_array<T>::value, int> = 0>
+inline bool copyArray(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>
-inline detail::enable_if_t<
-    !detail::is_base_of<JsonDocument, TDestination>::value, bool>
-copyArray(T (&src)[N], const TDestination& dst) {
+template <typename T, size_t N, typename TDestination,
+          detail::enable_if_t<
+              !detail::is_base_of<JsonDocument, TDestination>::value, int> = 0>
+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>
-inline detail::enable_if_t<
-    !detail::is_base_of<JsonDocument, TDestination>::value, bool>
-copyArray(const T* src, size_t len, const TDestination& dst) {
+template <typename T, typename TDestination,
+          detail::enable_if_t<
+              !detail::is_base_of<JsonDocument, TDestination>::value, int> = 0>
+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>
-inline detail::enable_if_t<!detail::is_array<T>::value, size_t> copyArray(
-    JsonVariantConst src, T& dst) {
+template <typename T, detail::enable_if_t<!detail::is_array<T>::value, int> = 0>
+inline size_t copyArray(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>
-inline detail::enable_if_t<detail::is_array<T>::value &&
-                               detail::is_base_of<JsonDocument, TSource>::value,
-                           size_t>
-copyArray(const TSource& src, T& dst) {
+template <
+    typename TSource, typename T,
+    detail::enable_if_t<detail::is_array<T>::value &&
+                            detail::is_base_of<JsonDocument, TSource>::value,
+                        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,
-          typename TStream, typename... Args,
-          typename = enable_if_t<  // issue #1897
-              !is_integral<typename first_or_void<Args...>::type>::value>>
+template <
+    template <typename> class TDeserializer, typename TDestination,
+    typename TStream, typename... Args,
+    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)),