From 81f7e9399d96c9b4f155e8f1b47a5b677777bddd Mon Sep 17 00:00:00 2001
From: Benoit Blanchon <git@benoitblanchon.fr>
Date: Fri, 20 Dec 2024 09:49:22 +0100
Subject: [PATCH] Move public facing SFINAEs to template declarations

---
 CHANGELOG.md                                  |   1 +
 src/ArduinoJson/Array/JsonArray.hpp           |  30 ++---
 src/ArduinoJson/Array/JsonArrayConst.hpp      |  12 +-
 src/ArduinoJson/Array/Utilities.hpp           |  38 +++---
 src/ArduinoJson/Document/JsonDocument.hpp     | 116 +++++++++---------
 src/ArduinoJson/Object/JsonObject.hpp         |  62 +++++-----
 src/ArduinoJson/Object/JsonObjectConst.hpp    |  34 ++---
 src/ArduinoJson/Variant/JsonVariantConst.hpp  |  65 +++++-----
 src/ArduinoJson/Variant/VariantOperators.hpp  |  42 +++----
 src/ArduinoJson/Variant/VariantRefBase.hpp    |  70 +++++------
 .../Variant/VariantRefBaseImpl.hpp            |  47 +++----
 11 files changed, 257 insertions(+), 260 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7bea7dd92..bccd0ef23 100644
--- a/CHANGELOG.md
+++ b/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
 >
diff --git a/src/ArduinoJson/Array/JsonArray.hpp b/src/ArduinoJson/Array/JsonArray.hpp
index 565cff26f..37c9ebfba 100644
--- a/src/ArduinoJson/Array/JsonArray.hpp
+++ b/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, short> = 0>
+  JsonVariant add() const {
     return JsonVariant(detail::ArrayData::addElement(data_, resources_),
                        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, short> = 0>
+  detail::ElementProxy<JsonArray> operator[](const TVariant& variant) const {
     if (variant.template is<size_t>())
       return {*this, variant.template as<size_t>()};
     else
diff --git a/src/ArduinoJson/Array/JsonArrayConst.hpp b/src/ArduinoJson/Array/JsonArrayConst.hpp
index 6b9db1925..739464fbe 100644
--- a/src/ArduinoJson/Array/JsonArrayConst.hpp
+++ b/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>
-  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_);
@@ -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>
-  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, short> = 0>
+  JsonVariantConst operator[](const TVariant& variant) const {
     if (variant.template is<size_t>())
       return operator[](variant.template as<size_t>());
     else
diff --git a/src/ArduinoJson/Array/Utilities.hpp b/src/ArduinoJson/Array/Utilities.hpp
index 9073468c8..2f0638f0e 100644
--- a/src/ArduinoJson/Array/Utilities.hpp
+++ b/src/ArduinoJson/Array/Utilities.hpp
@@ -11,27 +11,27 @@ 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,
+          typename = detail::enable_if_t<!detail::is_array<T>::value>>
+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,
+          typename = detail::enable_if_t<
+              !detail::is_base_of<JsonDocument, TDestination>::value>>
+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,
+          typename = detail::enable_if_t<
+              !detail::is_base_of<JsonDocument, TDestination>::value>>
+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 +62,9 @@ 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,
+          typename = detail::enable_if_t<!detail::is_array<T>::value>>
+inline size_t copyArray(JsonVariantConst src, T& dst) {
   dst = src.as<T>();
   return 1;
 }
@@ -102,11 +102,11 @@ 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,
+          typename = detail::enable_if_t<
+              detail::is_array<T>::value &&
+              detail::is_base_of<JsonDocument, TSource>::value>>
+inline size_t copyArray(const TSource& src, T& dst) {
   return copyArray(src.template as<JsonArrayConst>(), dst);
 }
 
diff --git a/src/ArduinoJson/Document/JsonDocument.hpp b/src/ArduinoJson/Document/JsonDocument.hpp
index 403930809..53dc82e68 100644
--- a/src/ArduinoJson/Document/JsonDocument.hpp
+++ b/src/ArduinoJson/Document/JsonDocument.hpp
@@ -36,14 +36,14 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   }
 
   // Construct from variant, array, or object
-  template <typename T>
-  JsonDocument(
-      const T& src, Allocator* alloc = detail::DefaultAllocator::instance(),
-      detail::enable_if_t<detail::IsVariant<T>::value ||
-                          detail::is_same<T, JsonArray>::value ||
-                          detail::is_same<T, JsonArrayConst>::value ||
-                          detail::is_same<T, JsonObject>::value ||
-                          detail::is_same<T, JsonObjectConst>::value>* = 0)
+  template <typename T, typename = detail::enable_if_t<
+                            detail::IsVariant<T>::value ||
+                            detail::is_same<T, JsonArray>::value ||
+                            detail::is_same<T, JsonArrayConst>::value ||
+                            detail::is_same<T, JsonObject>::value ||
+                            detail::is_same<T, JsonObjectConst>::value>>
+  JsonDocument(const T& src,
+               Allocator* alloc = detail::DefaultAllocator::instance())
       : JsonDocument(alloc) {
     set(src);
   }
@@ -136,9 +136,9 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Replaces the root with the specified value.
   // https://arduinojson.org/v7/api/jsondocument/set/
-  template <typename T>
-  detail::enable_if_t<!detail::is_base_of<JsonDocument, T>::value, bool> set(
-      const T& src) {
+  template <typename T, typename = detail::enable_if_t<
+                            !detail::is_base_of<JsonDocument, T>::value>>
+  bool set(const T& src) {
     return to<JsonVariant>().set(src);
   }
 
@@ -168,68 +168,65 @@ 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(
-      const TString& key) const {
+  bool containsKey(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, short> = 0>
   ARDUINOJSON_DEPRECATED("use doc[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
-      const TVariant& key) const {
+  bool containsKey(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>
-  detail::enable_if_t<
-      detail::IsString<TString>::value,
-      detail::MemberProxy<JsonDocument&, detail::AdaptedString<TString>>>
-  operator[](const TString& key) {
+  template <typename TString,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>>
+  detail::MemberProxy<JsonDocument&, detail::AdaptedString<TString>> 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>
-  detail::enable_if_t<
-      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
-      detail::MemberProxy<JsonDocument&, detail::AdaptedString<TChar*>>>
-  operator[](TChar* key) {
+  template <typename TChar,
+            typename = detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                           !detail::is_const<TChar>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
-  operator[](const TString& key) const {
+  template <typename TString,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
-                      JsonVariantConst>
-  operator[](TChar* key) const {
+  template <typename TChar,
+            typename = detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                           !detail::is_const<TChar>::value>>
+  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>
-  detail::enable_if_t<detail::is_integral<T>::value,
-                      detail::ElementProxy<JsonDocument&>>
-  operator[](T index) {
+  template <typename T,
+            detail::enable_if_t<detail::is_integral<T>::value, int> = 0>
+  detail::ElementProxy<JsonDocument&> operator[](T index) {
     return {*this, size_t(index)};
   }
 
@@ -241,9 +238,9 @@ 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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
-  operator[](const TVariant& key) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, short> = 0>
+  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 +251,18 @@ 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>
-  detail::enable_if_t<!detail::is_same<T, JsonVariant>::value, T> add() {
+  template <typename T, detail::enable_if_t<
+                            !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>
-  detail::enable_if_t<detail::is_same<T, JsonVariant>::value, T> add() {
+  template <typename T, detail::enable_if_t<
+                            detail::is_same<T, JsonVariant>::value, short> = 0>
+  JsonVariant add() {
     return JsonVariant(data_.addElement(&resources_), &resources_);
   }
 
@@ -284,36 +283,37 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Removes an element of the root array.
   // https://arduinojson.org/v7/api/jsondocument/remove/
-  template <typename T>
-  detail::enable_if_t<detail::is_integral<T>::value> remove(T index) {
+  template <typename T,
+            typename = detail::enable_if_t<detail::is_integral<T>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
-                      !detail::is_const<TChar>::value>
-  remove(TChar* key) {
+  template <typename TChar,
+            typename = detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                           !detail::is_const<TChar>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TString>::value> remove(
-      const TString& key) {
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
+  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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
-      const TVariant& key) {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, short> = 0>
+  void remove(const TVariant& key) {
     if (key.template is<const char*>())
       remove(key.template as<const char*>());
     if (key.template is<size_t>())
diff --git a/src/ArduinoJson/Object/JsonObject.hpp b/src/ArduinoJson/Object/JsonObject.hpp
index c90b29553..f74a1ab0e 100644
--- a/src/ArduinoJson/Object/JsonObject.hpp
+++ b/src/ArduinoJson/Object/JsonObject.hpp
@@ -101,31 +101,29 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
 
   // Gets or sets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobject/subscript/
-  template <typename TString>
-  detail::enable_if_t<
-      detail::IsString<TString>::value,
-      detail::MemberProxy<JsonObject, detail::AdaptedString<TString>>>
-  operator[](const TString& key) const {
+  template <typename TString,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>>
+  detail::MemberProxy<JsonObject, detail::AdaptedString<TString>> 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>
-  detail::enable_if_t<
-      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
-      detail::MemberProxy<JsonObject, detail::AdaptedString<TChar*>>>
-  operator[](TChar* key) const {
+  template <typename TChar,
+            typename = detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                           !detail::is_const<TChar>::value>>
+  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>
-  detail::enable_if_t<
-      detail::IsVariant<TVariant>::value,
-      detail::MemberProxy<JsonObject, detail::AdaptedString<JsonString>>>
-  operator[](const TVariant& key) const {
+  template <typename TVariant,
+            typename = detail::enable_if_t<detail::IsVariant<TVariant>::value>>
+  detail::MemberProxy<JsonObject, detail::AdaptedString<JsonString>> operator[](
+      const TVariant& key) const {
     return {*this, detail::adaptString(key.template as<JsonString>())};
   }
 
@@ -137,18 +135,18 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
 
   // Removes the member with the specified key.
   // https://arduinojson.org/v7/api/jsonobject/remove/
-  template <typename TString>
-  detail::enable_if_t<detail::IsString<TString>::value> remove(
-      const TString& key) const {
+  template <typename TString,
+            detail::enable_if_t<detail::IsString<TString>::value, int> = 0>
+  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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value> remove(
-      const TVariant& key) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, short> = 0>
+  void remove(const TVariant& key) const {
     if (key.template is<const char*>())
       remove(key.template as<const char*>());
   }
@@ -163,31 +161,33 @@ 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(
-      const TString& key) const {
+  bool containsKey(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,
+                                short> = 0>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
-                      bool> containsKey(TChar* key) const {
+  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,
+            typename = 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(
-      const TVariant& key) const {
+  bool containsKey(const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 
diff --git a/src/ArduinoJson/Object/JsonObjectConst.hpp b/src/ArduinoJson/Object/JsonObjectConst.hpp
index 91d9dca5c..63c2a82ef 100644
--- a/src/ArduinoJson/Object/JsonObjectConst.hpp
+++ b/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(
-      const TString& key) const {
+  bool containsKey(const TString& key) const {
     return detail::ObjectData::getMember(data_, detail::adaptString(key),
                                          resources_) != 0;
   }
@@ -89,18 +89,19 @@ 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, short> = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
-      const TVariant& key) const {
+  bool containsKey(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>
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
-  operator[](const TString& key) const {
+  template <typename TString,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>,
+            short = 1>
+  JsonVariantConst operator[](const TString& key) const {
     return JsonVariantConst(detail::ObjectData::getMember(
                                 data_, detail::adaptString(key), resources_),
                             resources_);
@@ -108,11 +109,10 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
 
   // Gets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobjectconst/subscript/
-  template <typename TChar>
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
-                      JsonVariantConst>
-  operator[](TChar* key) const {
+  template <typename TChar,
+            typename = detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                           !detail::is_const<TChar>::value>>
+  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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
-  operator[](const TVariant& key) const {
+  template <typename TVariant,
+            typename = detail::enable_if_t<detail::IsVariant<TVariant>::value>>
+  JsonVariantConst operator[](const TVariant& key) const {
     if (key.template is<JsonString>())
       return operator[](key.template as<JsonString>());
     else
diff --git a/src/ArduinoJson/Variant/JsonVariantConst.hpp b/src/ArduinoJson/Variant/JsonVariantConst.hpp
index f87b56ddb..5ab27df9c 100644
--- a/src/ArduinoJson/Variant/JsonVariantConst.hpp
+++ b/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>
+            typename = detail::enable_if_t<ConversionSupported<T>::value>>
   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>
+  template <typename T, typename = detail::enable_if_t<
+                            !ConversionSupported<T>::value, bool>>
   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>
-  detail::enable_if_t<ConversionSupported<T>::value, bool> is() const {
+  template <typename T,
+            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>
-  detail::enable_if_t<!ConversionSupported<T>::value, bool> is() const {
+  template <typename T,
+            detail::enable_if_t<!ConversionSupported<T>::value, short> = 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>
-  detail::enable_if_t<detail::is_integral<T>::value, JsonVariantConst>
-  operator[](T index) const {
+  template <typename T,
+            typename = detail::enable_if_t<detail::is_integral<T>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TString>::value, JsonVariantConst>
-  operator[](const TString& key) const {
+  template <typename TString,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>>
+  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>
-  detail::enable_if_t<detail::IsString<TChar*>::value &&
-                          !detail::is_const<TChar>::value,
-                      JsonVariantConst>
-  operator[](TChar* key) const {
+  template <typename TChar,
+            detail::enable_if_t<detail::IsString<TChar*>::value &&
+                                    !detail::is_const<TChar>::value,
+                                int> = 0>
+  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>
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, JsonVariantConst>
-  operator[](const TVariant& key) const {
+  template <typename TVariant,
+            detail::enable_if_t<detail::IsVariant<TVariant>::value, short> = 0>
+  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,
+            typename = detail::enable_if_t<detail::IsString<TString>::value>>
   ARDUINOJSON_DEPRECATED("use var[key].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TString>::value, bool> containsKey(
-      const TString& key) const {
+  bool containsKey(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 &&
-                          !detail::is_const<TChar>::value,
-                      bool> containsKey(TChar* key) const {
+  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, short> = 0>
   ARDUINOJSON_DEPRECATED("use var[key].is<T>() instead")
-  detail::enable_if_t<detail::IsVariant<TVariant>::value, bool> containsKey(
-      const TVariant& key) const {
+  bool containsKey(const TVariant& key) const {
     return containsKey(key.template as<const char*>());
   }
 
diff --git a/src/ArduinoJson/Variant/VariantOperators.hpp b/src/ArduinoJson/Variant/VariantOperators.hpp
index 08e5bbd4f..25b9a5d0c 100644
--- a/src/ArduinoJson/Variant/VariantOperators.hpp
+++ b/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>
-  friend enable_if_t<!IsVariant<T>::value && !is_array<T>::value, T> operator|(
-      const TVariant& variant, const T& defaultValue) {
+  template <typename T,
+            typename = enable_if_t<!IsVariant<T>::value && !is_array<T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
-  operator==(const TVariant& lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
-  operator!=(TVariant lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool> operator<(
-      TVariant lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
-  operator<=(TVariant lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool> operator>(
-      TVariant lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  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>
-  friend enable_if_t<!is_base_of<VariantOperatorTag, T>::value, bool>
-  operator>=(const TVariant& lhs, const T& rhs) {
+  template <typename T,
+            typename = enable_if_t<!is_base_of<VariantOperatorTag, T>::value>>
+  friend bool operator>=(const TVariant& lhs, const T& rhs) {
     return (compare(lhs, rhs) & COMPARE_RESULT_GREATER_OR_EQUAL) != 0;
   }
 };
diff --git a/src/ArduinoJson/Variant/VariantRefBase.hpp b/src/ArduinoJson/Variant/VariantRefBase.hpp
index 30ee3e3e0..ea701ea45 100644
--- a/src/ArduinoJson/Variant/VariantRefBase.hpp
+++ b/src/ArduinoJson/Variant/VariantRefBase.hpp
@@ -55,18 +55,18 @@ class VariantRefBase : public VariantTag {
 
   // Sets the value to an empty array.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
-  enable_if_t<is_same<T, JsonArray>::value, JsonArray> to() const;
+  template <typename T, enable_if_t<is_same<T, JsonArray>::value, long> = 0>
+  JsonArray to() const;
 
   // Sets the value to an empty object.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
-  enable_if_t<is_same<T, JsonObject>::value, JsonObject> to() const;
+  template <typename T, enable_if_t<is_same<T, JsonObject>::value, short> = 0>
+  JsonObject to() const;
 
   // Sets the value to null.
   // https://arduinojson.org/v7/api/jsonvariant/to/
-  template <typename T>
-  enable_if_t<is_same<T, JsonVariant>::value, JsonVariant> to() const;
+  template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int> = 0>
+  JsonVariant to() const;
 
   // Returns true if the value is of the specified type.
   // https://arduinojson.org/v7/api/jsonvariant/is/
@@ -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>
-  enable_if_t<!is_same<T, JsonVariant>::value, T> add() const {
+  template <typename T, enable_if_t<!is_same<T, JsonVariant>::value, int> = 0>
+  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>
-  enable_if_t<is_same<T, JsonVariant>::value, T> add() const;
+  template <typename T, enable_if_t<is_same<T, JsonVariant>::value, short> = 0>
+  T add() const;
 
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonvariant/add/
@@ -140,24 +140,25 @@ class VariantRefBase : public VariantTag {
 
   // Removes a member of the object.
   // https://arduinojson.org/v7/api/jsonvariant/remove/
-  template <typename TChar>
-  enable_if_t<IsString<TChar*>::value> remove(TChar* key) const {
+  template <typename TChar, typename = enable_if_t<IsString<TChar*>::value>>
+  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>
-  enable_if_t<IsString<TString>::value> remove(const TString& key) const {
+  template <typename TString, enable_if_t<IsString<TString>::value, int> = 0>
+  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>
-  enable_if_t<IsVariant<TVariant>::value> remove(const TVariant& key) const {
+  template <typename TVariant,
+            enable_if_t<IsVariant<TVariant>::value, short> = 0>
+  void remove(const TVariant& key) const {
     if (key.template is<size_t>())
       remove(key.template as<size_t>());
     else
@@ -170,43 +171,42 @@ 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(
-      const TString& key) const;
+  bool containsKey(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, short> = 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,
+            typename = enable_if_t<IsVariant<TVariant>::value>, int = 0>
   ARDUINOJSON_DEPRECATED("use obj[key].is<T>() instead")
-  enable_if_t<IsVariant<TVariant>::value, bool> containsKey(
-      const TVariant& key) const;
+  bool containsKey(const TVariant& key) const;
 
   // Gets or sets an object member.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
-  template <typename TString>
-  FORCE_INLINE enable_if_t<IsString<TString>::value,
-                           MemberProxy<TDerived, AdaptedString<TString>>>
-  operator[](const TString& key) const;
+  template <typename TString, enable_if_t<IsString<TString>::value, int> = 0>
+  FORCE_INLINE MemberProxy<TDerived, AdaptedString<TString>> operator[](
+      const TString& key) const;
 
   // Gets or sets an object member.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
-  template <typename TChar>
-  FORCE_INLINE enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
-                           MemberProxy<TDerived, AdaptedString<TChar*>>>
-  operator[](TChar* key) const;
+  template <typename TChar,
+            enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
+                        short> = 0>
+  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>
-  enable_if_t<IsVariant<TVariant>::value, JsonVariantConst> operator[](
-      const TVariant& key) const {
+  template <typename TVariant,
+            typename = enable_if_t<IsVariant<TVariant>::value>>
+  JsonVariantConst operator[](const TVariant& key) const {
     if (key.template is<size_t>())
       return operator[](key.template as<size_t>());
     else
diff --git a/src/ArduinoJson/Variant/VariantRefBaseImpl.hpp b/src/ArduinoJson/Variant/VariantRefBaseImpl.hpp
index f69e01d3e..ec871ddeb 100644
--- a/src/ArduinoJson/Variant/VariantRefBaseImpl.hpp
+++ b/src/ArduinoJson/Variant/VariantRefBaseImpl.hpp
@@ -67,34 +67,30 @@ inline void convertToJson(const VariantRefBase<TDerived>& src,
 }
 
 template <typename TDerived>
-template <typename T>
-inline enable_if_t<is_same<T, JsonVariant>::value, T>
-VariantRefBase<TDerived>::add() const {
+template <typename T, enable_if_t<is_same<T, JsonVariant>::value, short>>
+inline T VariantRefBase<TDerived>::add() const {
   return JsonVariant(
       detail::VariantData::addElement(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename TString>
-inline enable_if_t<IsString<TString>::value, bool>
-VariantRefBase<TDerived>::containsKey(const TString& key) const {
+template <typename TString, enable_if_t<IsString<TString>::value, int>>
+inline bool VariantRefBase<TDerived>::containsKey(const TString& key) const {
   return VariantData::getMember(getData(), adaptString(key),
                                 getResourceManager()) != 0;
 }
 
 template <typename TDerived>
-template <typename TChar>
-inline enable_if_t<IsString<TChar*>::value, bool>
-VariantRefBase<TDerived>::containsKey(TChar* key) const {
+template <typename TChar, enable_if_t<IsString<TChar*>::value, short>>
+inline bool VariantRefBase<TDerived>::containsKey(TChar* key) const {
   return VariantData::getMember(getData(), adaptString(key),
                                 getResourceManager()) != 0;
 }
 
 template <typename TDerived>
-template <typename TVariant>
-inline enable_if_t<IsVariant<TVariant>::value, bool>
-VariantRefBase<TDerived>::containsKey(const TVariant& key) const {
+template <typename TVariant, typename, int>
+inline bool VariantRefBase<TDerived>::containsKey(const TVariant& key) const {
   return containsKey(key.template as<const char*>());
 }
 
@@ -123,17 +119,17 @@ inline ElementProxy<TDerived> VariantRefBase<TDerived>::operator[](
 }
 
 template <typename TDerived>
-template <typename TChar>
-inline enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
-                   MemberProxy<TDerived, AdaptedString<TChar*>>>
+template <
+    typename TChar,
+    enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value, short>>
+inline MemberProxy<TDerived, AdaptedString<TChar*>>
 VariantRefBase<TDerived>::operator[](TChar* key) const {
   return {derived(), adaptString(key)};
 }
 
 template <typename TDerived>
-template <typename TString>
-inline enable_if_t<IsString<TString>::value,
-                   MemberProxy<TDerived, AdaptedString<TString>>>
+template <typename TString, enable_if_t<IsString<TString>::value, int>>
+inline MemberProxy<TDerived, AdaptedString<TString>>
 VariantRefBase<TDerived>::operator[](const TString& key) const {
   return {derived(), adaptString(key)};
 }
@@ -153,27 +149,24 @@ inline bool VariantRefBase<TDerived>::doSet(const T& value, true_type) const {
 }
 
 template <typename TDerived>
-template <typename T>
-inline enable_if_t<is_same<T, JsonArray>::value, JsonArray>
-VariantRefBase<TDerived>::to() const {
+template <typename T, enable_if_t<is_same<T, JsonArray>::value, long>>
+inline JsonArray VariantRefBase<TDerived>::to() const {
   return JsonArray(
       VariantData::toArray(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename T>
-enable_if_t<is_same<T, JsonObject>::value, JsonObject>
-VariantRefBase<TDerived>::to() const {
+template <typename T, enable_if_t<is_same<T, JsonObject>::value, short>>
+JsonObject VariantRefBase<TDerived>::to() const {
   return JsonObject(
       VariantData::toObject(getOrCreateData(), getResourceManager()),
       getResourceManager());
 }
 
 template <typename TDerived>
-template <typename T>
-enable_if_t<is_same<T, JsonVariant>::value, JsonVariant>
-VariantRefBase<TDerived>::to() const {
+template <typename T, enable_if_t<is_same<T, JsonVariant>::value, int>>
+JsonVariant VariantRefBase<TDerived>::to() const {
   auto data = getOrCreateData();
   auto resources = getResourceManager();
   detail::VariantData::clear(data, resources);