Added a return value to visitors

src/ArduinoJson/Array/ArrayFunctions.hpp

@@ -12,12 +12,13 @@ inline VariantData *arrayAdd(CollectionData *arr, MemoryPool *pool) {
   return arr ? arr->addElement(pool) : 0;
 }
 
-template <typename Visitor>
-inline void arrayAccept(const CollectionData *arr, Visitor &visitor) {
+template <typename TVisitor>
+inline typename TVisitor::result_type arrayAccept(const CollectionData *arr,
+                                                  TVisitor &visitor) {
   if (arr)
-    visitor.visitArray(*arr);
+    return visitor.visitArray(*arr);
   else
-    visitor.visitNull();
+    return visitor.visitNull();
 }
 
 inline bool arrayEquals(const CollectionData *lhs, const CollectionData *rhs) {

src/ArduinoJson/Array/ArrayRef.hpp

@@ -27,9 +27,9 @@ class ArrayRefBase {
     return VariantConstRef(reinterpret_cast<const VariantData*>(data));
   }
 
-  template <typename Visitor>
-  FORCE_INLINE void accept(Visitor& visitor) const {
-    arrayAccept(_data, visitor);
+  template <typename TVisitor>
+  FORCE_INLINE typename TVisitor::result_type accept(TVisitor& visitor) const {
+    return arrayAccept(_data, visitor);
   }
 
   FORCE_INLINE bool isNull() const {

src/ArduinoJson/Array/ElementProxy.hpp

@@ -98,8 +98,8 @@ class ElementProxy : public VariantOperators<ElementProxy<TArray> >,
     return getOrAddUpstreamElement().set(value);
   }
 
-  template <typename Visitor>
-  void accept(Visitor& visitor) const {
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor& visitor) const {
     return getUpstreamElement().accept(visitor);
   }
 

src/ArduinoJson/Array/Utilities.hpp

@@ -65,40 +65,61 @@ inline bool copyArray(T (&src)[N1][N2], JsonDocument& dst) {
 }
 
 template <typename T>
-class ArrayCopier1D {
+class ArrayCopier1D : public Visitor<size_t> {
  public:
   ArrayCopier1D(T* destination, size_t capacity)
-      : _destination(destination), _capacity(capacity), _size(0) {}
+      : _destination(destination), _capacity(capacity) {}
 
-  void visitArray(const CollectionData& array) {
+  size_t visitArray(const CollectionData& array) {
+    size_t size = 0;
     VariantSlot* slot = array.head();
 
-    while (slot != 0 && _size < _capacity) {
-      _destination[_size++] = variantAs<T>(slot->data());
+    while (slot != 0 && size < _capacity) {
+      _destination[size++] = variantAs<T>(slot->data());
       slot = slot->next();
     }
+    return size;
   }
-  void visitObject(const CollectionData&) {}
-  void visitFloat(Float) {}
-  void visitString(const char*) {}
-  void visitRawJson(const char*, size_t) {}
-  void visitNegativeInteger(UInt) {}
-  void visitPositiveInteger(UInt) {}
-  void visitBoolean(bool) {}
-  void visitNull() {}
 
-  size_t result() const {
-    return _size;
+  size_t visitObject(const CollectionData&) {
+    return 0;
+  }
+
+  size_t visitFloat(Float) {
+    return 0;
+  }
+
+  size_t visitString(const char*) {
+    return 0;
+  }
+
+  size_t visitRawJson(const char*, size_t) {
+    return 0;
+  }
+
+  size_t visitNegativeInteger(UInt) {
+    return 0;
+  }
+
+  size_t visitPositiveInteger(UInt) {
+    return 0;
+  }
+
+  size_t visitBoolean(bool) {
+    return 0;
+  }
+
+  size_t visitNull() {
+    return 0;
   }
 
  private:
   T* _destination;
   size_t _capacity;
-  size_t _size;
 };
 
 template <typename T, size_t N1, size_t N2>
-class ArrayCopier2D {
+class ArrayCopier2D : public Visitor<void> {
  public:
   ArrayCopier2D(T (*destination)[N1][N2]) : _destination(destination) {}
 
@@ -136,8 +157,8 @@ inline typename enable_if<!is_array<T>::value, size_t>::type copyArray(
 template <typename TSource, typename T>
 inline size_t copyArray(const TSource& src, T* dst, size_t len) {
   ArrayCopier1D<T> copier(dst, len);
-  src.accept(copier);
-  return copier.result();
+
+  return src.accept(copier);
 }
 
 // Copy a JsonArray to a 2D array

src/ArduinoJson/Document/JsonDocument.hpp

@@ -15,8 +15,8 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class JsonDocument : public Visitable {
  public:
-  template <typename Visitor>
-  void accept(Visitor& visitor) const {
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor& visitor) const {
     return getVariant().accept(visitor);
   }
 

src/ArduinoJson/Json/JsonSerializer.hpp

@@ -12,11 +12,11 @@
 namespace ARDUINOJSON_NAMESPACE {
 
 template <typename TWriter>
-class JsonSerializer {
+class JsonSerializer : public Visitor<size_t> {
  public:
   JsonSerializer(TWriter writer) : _formatter(writer) {}
 
-  FORCE_INLINE void visitArray(const CollectionData &array) {
+  FORCE_INLINE size_t visitArray(const CollectionData &array) {
     write('[');
 
     VariantSlot *slot = array.head();
@@ -32,9 +32,10 @@ class JsonSerializer {
     }
 
     write(']');
+    return bytesWritten();
   }
 
-  void visitObject(const CollectionData &object) {
+  size_t visitObject(const CollectionData &object) {
     write('{');
 
     VariantSlot *slot = object.head();
@@ -52,41 +53,49 @@ class JsonSerializer {
     }
 
     write('}');
+    return bytesWritten();
   }
 
-  void visitFloat(Float value) {
+  size_t visitFloat(Float value) {
     _formatter.writeFloat(value);
+    return bytesWritten();
   }
 
-  void visitString(const char *value) {
+  size_t visitString(const char *value) {
     _formatter.writeString(value);
+    return bytesWritten();
   }
 
-  void visitRawJson(const char *data, size_t n) {
+  size_t visitRawJson(const char *data, size_t n) {
     _formatter.writeRaw(data, n);
+    return bytesWritten();
   }
 
-  void visitNegativeInteger(UInt value) {
+  size_t visitNegativeInteger(UInt value) {
     _formatter.writeNegativeInteger(value);
+    return bytesWritten();
   }
 
-  void visitPositiveInteger(UInt value) {
+  size_t visitPositiveInteger(UInt value) {
     _formatter.writePositiveInteger(value);
+    return bytesWritten();
   }
 
-  void visitBoolean(bool value) {
+  size_t visitBoolean(bool value) {
     _formatter.writeBoolean(value);
+    return bytesWritten();
   }
 
-  void visitNull() {
+  size_t visitNull() {
     _formatter.writeRaw("null");
+    return bytesWritten();
   }
 
+ protected:
   size_t bytesWritten() const {
     return _formatter.bytesWritten();
   }
 
- protected:
   void write(char c) {
     _formatter.writeRaw(c);
   }

src/ArduinoJson/Json/PrettyJsonSerializer.hpp

@@ -18,44 +18,48 @@ class PrettyJsonSerializer : public JsonSerializer<TWriter> {
  public:
   PrettyJsonSerializer(TWriter &writer) : base(writer), _nesting(0) {}
 
-  void visitArray(const CollectionData &array) {
+  size_t visitArray(const CollectionData &array) {
     VariantSlot *slot = array.head();
-    if (!slot)
-      return base::write("[]");
+    if (slot) {
+      base::write("[\r\n");
+      _nesting++;
+      while (slot != 0) {
+        indent();
+        slot->data()->accept(*this);
 
-    base::write("[\r\n");
-    _nesting++;
-    while (slot != 0) {
+        slot = slot->next();
+        base::write(slot ? ",\r\n" : "\r\n");
+      }
+      _nesting--;
       indent();
-      slot->data()->accept(*this);
-
-      slot = slot->next();
-      base::write(slot ? ",\r\n" : "\r\n");
+      base::write("]");
+    } else {
+      base::write("[]");
     }
-    _nesting--;
-    indent();
-    base::write("]");
+    return this->bytesWritten();
   }
 
-  void visitObject(const CollectionData &object) {
+  size_t visitObject(const CollectionData &object) {
     VariantSlot *slot = object.head();
-    if (!slot)
-      return base::write("{}");
+    if (slot) {
+      base::write("{\r\n");
+      _nesting++;
+      while (slot != 0) {
+        indent();
+        base::visitString(slot->key());
+        base::write(": ");
+        slot->data()->accept(*this);
 
-    base::write("{\r\n");
-    _nesting++;
-    while (slot != 0) {
+        slot = slot->next();
+        base::write(slot ? ",\r\n" : "\r\n");
+      }
+      _nesting--;
       indent();
-      base::visitString(slot->key());
-      base::write(": ");
-      slot->data()->accept(*this);
-
-      slot = slot->next();
-      base::write(slot ? ",\r\n" : "\r\n");
+      base::write("}");
+    } else {
+      base::write("{}");
     }
-    _nesting--;
-    indent();
-    base::write("}");
+    return this->bytesWritten();
   }
 
  private:

src/ArduinoJson/Json/TextFormatter.hpp

@@ -12,17 +12,18 @@
 #include <ArduinoJson/Numbers/Integer.hpp>
 #include <ArduinoJson/Polyfills/assert.hpp>
 #include <ArduinoJson/Polyfills/attributes.hpp>
+#include <ArduinoJson/Serialization/CountingDecorator.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
 template <typename TWriter>
 class TextFormatter {
  public:
-  explicit TextFormatter(TWriter writer) : _writer(writer), _length(0) {}
+  explicit TextFormatter(TWriter writer) : _writer(writer) {}
 
   // Returns the number of bytes sent to the TWriter implementation.
   size_t bytesWritten() const {
-    return _length;
+    return _writer.count();
   }
 
   void writeBoolean(bool value) {
@@ -128,28 +129,28 @@ class TextFormatter {
   }
 
   void writeRaw(const char *s) {
-    _length += _writer.write(reinterpret_cast<const uint8_t *>(s), strlen(s));
+    _writer.write(reinterpret_cast<const uint8_t *>(s), strlen(s));
   }
 
   void writeRaw(const char *s, size_t n) {
-    _length += _writer.write(reinterpret_cast<const uint8_t *>(s), n);
+    _writer.write(reinterpret_cast<const uint8_t *>(s), n);
   }
 
   void writeRaw(const char *begin, const char *end) {
-    _length += _writer.write(reinterpret_cast<const uint8_t *>(begin),
-                             static_cast<size_t>(end - begin));
+    _writer.write(reinterpret_cast<const uint8_t *>(begin),
+                  static_cast<size_t>(end - begin));
   }
 
   template <size_t N>
   void writeRaw(const char (&s)[N]) {
-    _length += _writer.write(reinterpret_cast<const uint8_t *>(s), N - 1);
+    _writer.write(reinterpret_cast<const uint8_t *>(s), N - 1);
   }
   void writeRaw(char c) {
-    _length += _writer.write(static_cast<uint8_t>(c));
+    _writer.write(static_cast<uint8_t>(c));
   }
 
  protected:
-  TWriter _writer;
+  CountingDecorator<TWriter> _writer;
   size_t _length;
 
  private:

src/ArduinoJson/Misc/Visitable.hpp

@@ -8,6 +8,11 @@
 
 namespace ARDUINOJSON_NAMESPACE {
 
+template <typename TResult>
+struct Visitor {
+  typedef TResult result_type;
+};
+
 struct Visitable {
   // template<Visitor>
   // void accept(Visitor&) const;

src/ArduinoJson/MsgPack/MsgPackSerializer.hpp

@@ -7,6 +7,7 @@
 #include <ArduinoJson/MsgPack/endianess.hpp>
 #include <ArduinoJson/Polyfills/assert.hpp>
 #include <ArduinoJson/Polyfills/type_traits.hpp>
+#include <ArduinoJson/Serialization/CountingDecorator.hpp>
 #include <ArduinoJson/Serialization/measure.hpp>
 #include <ArduinoJson/Serialization/serialize.hpp>
 #include <ArduinoJson/Variant/VariantData.hpp>
@@ -14,19 +15,20 @@
 namespace ARDUINOJSON_NAMESPACE {
 
 template <typename TWriter>
-class MsgPackSerializer {
+class MsgPackSerializer : public Visitor<size_t> {
  public:
-  MsgPackSerializer(TWriter writer) : _writer(writer), _bytesWritten(0) {}
+  MsgPackSerializer(TWriter writer) : _writer(writer) {}
 
   template <typename T>
-  typename enable_if<sizeof(T) == 4>::type visitFloat(T value32) {
+  typename enable_if<sizeof(T) == 4, size_t>::type visitFloat(T value32) {
     writeByte(0xCA);
     writeInteger(value32);
+    return bytesWritten();
   }
 
   template <typename T>
   ARDUINOJSON_NO_SANITIZE("float-cast-overflow")
-  typename enable_if<sizeof(T) == 8>::type visitFloat(T value64) {
+  typename enable_if<sizeof(T) == 8, size_t>::type visitFloat(T value64) {
     float value32 = float(value64);
     if (value32 == value64) {
       writeByte(0xCA);
@@ -35,9 +37,10 @@ class MsgPackSerializer {
       writeByte(0xCB);
       writeInteger(value64);
     }
+    return bytesWritten();
   }
 
-  void visitArray(const CollectionData& array) {
+  size_t visitArray(const CollectionData& array) {
     size_t n = array.size();
     if (n < 0x10) {
       writeByte(uint8_t(0x90 + array.size()));
@@ -51,9 +54,10 @@ class MsgPackSerializer {
     for (VariantSlot* slot = array.head(); slot; slot = slot->next()) {
       slot->data()->accept(*this);
     }
+    return bytesWritten();
   }
 
-  void visitObject(const CollectionData& object) {
+  size_t visitObject(const CollectionData& object) {
     size_t n = object.size();
     if (n < 0x10) {
       writeByte(uint8_t(0x80 + n));
@@ -68,9 +72,10 @@ class MsgPackSerializer {
       visitString(slot->key());
       slot->data()->accept(*this);
     }
+    return bytesWritten();
   }
 
-  void visitString(const char* value) {
+  size_t visitString(const char* value) {
     ARDUINOJSON_ASSERT(value != NULL);
 
     size_t n = strlen(value);
@@ -88,13 +93,15 @@ class MsgPackSerializer {
       writeInteger(uint32_t(n));
     }
     writeBytes(reinterpret_cast<const uint8_t*>(value), n);
+    return bytesWritten();
   }
 
-  void visitRawJson(const char* data, size_t size) {
+  size_t visitRawJson(const char* data, size_t size) {
     writeBytes(reinterpret_cast<const uint8_t*>(data), size);
+    return bytesWritten();
   }
 
-  void visitNegativeInteger(UInt value) {
+  size_t visitNegativeInteger(UInt value) {
     UInt negated = UInt(~value + 1);
     if (value <= 0x20) {
       writeInteger(int8_t(negated));
@@ -114,9 +121,10 @@ class MsgPackSerializer {
       writeInteger(int64_t(negated));
     }
 #endif
+    return bytesWritten();
   }
 
-  void visitPositiveInteger(UInt value) {
+  size_t visitPositiveInteger(UInt value) {
     if (value <= 0x7F) {
       writeInteger(uint8_t(value));
     } else if (value <= 0xFF) {
@@ -141,27 +149,30 @@ class MsgPackSerializer {
       writeInteger(uint64_t(value));
     }
 #endif
+    return bytesWritten();
   }
 
-  void visitBoolean(bool value) {
+  size_t visitBoolean(bool value) {
     writeByte(value ? 0xC3 : 0xC2);
+    return bytesWritten();
   }
 
-  void visitNull() {
+  size_t visitNull() {
     writeByte(0xC0);
-  }
-
-  size_t bytesWritten() const {
-    return _bytesWritten;
+    return bytesWritten();
   }
 
  private:
+  size_t bytesWritten() const {
+    return _writer.count();
+  }
+
   void writeByte(uint8_t c) {
-    _bytesWritten += _writer.write(c);
+    _writer.write(c);
   }
 
   void writeBytes(const uint8_t* p, size_t n) {
-    _bytesWritten += _writer.write(p, n);
+    _writer.write(p, n);
   }
 
   template <typename T>
@@ -170,8 +181,7 @@ class MsgPackSerializer {
     writeBytes(reinterpret_cast<uint8_t*>(&value), sizeof(value));
   }
 
-  TWriter _writer;
-  size_t _bytesWritten;
+  CountingDecorator<TWriter> _writer;
 };
 
 template <typename TSource, typename TDestination>

src/ArduinoJson/Object/MemberProxy.hpp

@@ -120,8 +120,8 @@ class MemberProxy : public VariantOperators<MemberProxy<TObject, TStringRef> >,
     return getOrAddUpstreamMember().set(value);
   }
 
-  template <typename Visitor>
-  void accept(Visitor &visitor) const {
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor &visitor) const {
     return getUpstreamMember().accept(visitor);
   }
 

src/ArduinoJson/Object/ObjectFunctions.hpp

@@ -8,12 +8,13 @@
 
 namespace ARDUINOJSON_NAMESPACE {
 
-template <typename Visitor>
-void objectAccept(const CollectionData *obj, Visitor &visitor) {
+template <typename TVisitor>
+typename TVisitor::result_type objectAccept(const CollectionData *obj,
+                                            TVisitor &visitor) {
   if (obj)
-    visitor.visitObject(*obj);
+    return visitor.visitObject(*obj);
   else
-    visitor.visitNull();
+    return visitor.visitNull();
 }
 
 inline bool objectEquals(const CollectionData *lhs, const CollectionData *rhs) {

src/ArduinoJson/Object/ObjectRef.hpp

@@ -22,9 +22,9 @@ class ObjectRefBase {
     return VariantConstRef(reinterpret_cast<const VariantData*>(data));
   }
 
-  template <typename Visitor>
-  FORCE_INLINE void accept(Visitor& visitor) const {
-    objectAccept(_data, visitor);
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor& visitor) const {
+    return objectAccept(_data, visitor);
   }
 
   FORCE_INLINE bool isNull() const {

src/ArduinoJson/Serialization/CountingDecorator.hpp

@@ -0,0 +1,33 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+template <typename TWriter>
+class CountingDecorator {
+ public:
+  explicit CountingDecorator(TWriter& writer) : _writer(writer), _count(0) {}
+
+  void write(uint8_t c) {
+    _count += _writer.write(c);
+  }
+
+  void write(const uint8_t* s, size_t n) {
+    _count += _writer.write(s, n);
+  }
+
+  size_t count() const {
+    return _count;
+  }
+
+ private:
+  TWriter _writer;
+  size_t _count;
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/measure.hpp

@@ -12,8 +12,7 @@ template <template <typename> class TSerializer, typename TSource>
 size_t measure(const TSource &source) {
   DummyWriter dp;
   TSerializer<DummyWriter> serializer(dp);
-  source.accept(serializer);
-  return serializer.bytesWritten();
+  return source.accept(serializer);
 }
 
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/serialize.hpp

@@ -12,8 +12,7 @@ template <template <typename> class TSerializer, typename TSource,
           typename TWriter>
 size_t doSerialize(const TSource &source, TWriter writer) {
   TSerializer<TWriter> serializer(writer);
-  source.accept(serializer);
-  return serializer.bytesWritten();
+  return source.accept(serializer);
 }
 
 template <template <typename> class TSerializer, typename TSource,

src/ArduinoJson/Variant/VariantCompare.hpp

@@ -14,20 +14,34 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class CollectionData;
 
-struct ComparerBase {
-  CompareResult result;
-
-  ComparerBase() : result(COMPARE_RESULT_DIFFER) {}
-
-  void visitArray(const CollectionData &) {}
-  void visitBoolean(bool) {}
-  void visitFloat(Float) {}
-  void visitNegativeInteger(UInt) {}
-  void visitNull() {}
-  void visitObject(const CollectionData &) {}
-  void visitPositiveInteger(UInt) {}
-  void visitRawJson(const char *, size_t) {}
-  void visitString(const char *) {}
+struct ComparerBase : Visitor<CompareResult> {
+  CompareResult visitArray(const CollectionData &) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitBoolean(bool) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitFloat(Float) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitNegativeInteger(UInt) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitNull() {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitObject(const CollectionData &) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitPositiveInteger(UInt) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitRawJson(const char *, size_t) {
+    return COMPARE_RESULT_DIFFER;
+  }
+  CompareResult visitString(const char *) {
+    return COMPARE_RESULT_DIFFER;
+  }
 };
 
 template <typename T, typename Enable = void>
@@ -40,19 +54,21 @@ struct Comparer<T, typename enable_if<IsString<T>::value>::type>
 
   explicit Comparer(T value) : rhs(value) {}
 
-  void visitString(const char *lhs) {
+  CompareResult visitString(const char *lhs) {
     int i = adaptString(rhs).compare(lhs);
     if (i < 0)
-      result = COMPARE_RESULT_GREATER;
+      return COMPARE_RESULT_GREATER;
     else if (i > 0)
-      result = COMPARE_RESULT_LESS;
+      return COMPARE_RESULT_LESS;
     else
-      result = COMPARE_RESULT_EQUAL;
+      return COMPARE_RESULT_EQUAL;
   }
 
-  void visitNull() {
+  CompareResult visitNull() {
     if (adaptString(rhs).isNull())
-      result = COMPARE_RESULT_EQUAL;
+      return COMPARE_RESULT_EQUAL;
+    else
+      return COMPARE_RESULT_DIFFER;
   }
 };
 
@@ -64,26 +80,26 @@ struct Comparer<T, typename enable_if<is_integral<T>::value ||
 
   explicit Comparer(T value) : rhs(value) {}
 
-  void visitFloat(Float lhs) {
-    result = arithmeticCompare(lhs, rhs);
+  CompareResult visitFloat(Float lhs) {
+    return arithmeticCompare(lhs, rhs);
   }
 
-  void visitNegativeInteger(UInt lhs) {
-    result = arithmeticCompareNegateLeft(lhs, rhs);
+  CompareResult visitNegativeInteger(UInt lhs) {
+    return arithmeticCompareNegateLeft(lhs, rhs);
   }
 
-  void visitPositiveInteger(UInt lhs) {
-    result = arithmeticCompare(lhs, rhs);
+  CompareResult visitPositiveInteger(UInt lhs) {
+    return arithmeticCompare(lhs, rhs);
   }
 
-  void visitBoolean(bool lhs) {
-    visitPositiveInteger(static_cast<UInt>(lhs));
+  CompareResult visitBoolean(bool lhs) {
+    return visitPositiveInteger(static_cast<UInt>(lhs));
   }
 };
 
 struct NullComparer : ComparerBase {
-  void visitNull() {
-    result = COMPARE_RESULT_EQUAL;
+  CompareResult visitNull() {
+    return COMPARE_RESULT_EQUAL;
   }
 };
 
@@ -99,9 +115,11 @@ struct ArrayComparer : ComparerBase {
 
   explicit ArrayComparer(const CollectionData &rhs) : _rhs(&rhs) {}
 
-  void visitArray(const CollectionData &lhs) {
+  CompareResult visitArray(const CollectionData &lhs) {
     if (lhs.equalsArray(*_rhs))
-      result = COMPARE_RESULT_EQUAL;
+      return COMPARE_RESULT_EQUAL;
+    else
+      return COMPARE_RESULT_DIFFER;
   }
 };
 
@@ -110,20 +128,20 @@ struct NegativeIntegerComparer : ComparerBase {
 
   explicit NegativeIntegerComparer(UInt rhs) : _rhs(rhs) {}
 
-  void visitFloat(Float lhs) {
-    result = arithmeticCompareNegateRight(lhs, _rhs);
+  CompareResult visitFloat(Float lhs) {
+    return arithmeticCompareNegateRight(lhs, _rhs);
   }
 
-  void visitNegativeInteger(UInt lhs) {
-    result = arithmeticCompare(_rhs, lhs);
+  CompareResult visitNegativeInteger(UInt lhs) {
+    return arithmeticCompare(_rhs, lhs);
   }
 
-  void visitPositiveInteger(UInt) {
-    result = COMPARE_RESULT_GREATER;
+  CompareResult visitPositiveInteger(UInt) {
+    return COMPARE_RESULT_GREATER;
   }
 
-  void visitBoolean(bool) {
-    result = COMPARE_RESULT_GREATER;
+  CompareResult visitBoolean(bool) {
+    return COMPARE_RESULT_GREATER;
   }
 };
 
@@ -132,9 +150,11 @@ struct ObjectComparer : ComparerBase {
 
   explicit ObjectComparer(const CollectionData &rhs) : _rhs(&rhs) {}
 
-  void visitObject(const CollectionData &lhs) {
+  CompareResult visitObject(const CollectionData &lhs) {
     if (lhs.equalsObject(*_rhs))
-      result = COMPARE_RESULT_EQUAL;
+      return COMPARE_RESULT_EQUAL;
+    else
+      return COMPARE_RESULT_DIFFER;
   }
 };
 
@@ -145,15 +165,15 @@ struct RawComparer : ComparerBase {
   explicit RawComparer(const char *rhsData, size_t rhsSize)
       : _rhsData(rhsData), _rhsSize(rhsSize) {}
 
-  void visitRawJson(const char *lhsData, size_t lhsSize) {
+  CompareResult visitRawJson(const char *lhsData, size_t lhsSize) {
     size_t size = _rhsSize < lhsSize ? _rhsSize : lhsSize;
     int n = memcmp(lhsData, _rhsData, size);
     if (n < 0)
-      result = COMPARE_RESULT_LESS;
+      return COMPARE_RESULT_LESS;
     else if (n > 0)
-      result = COMPARE_RESULT_GREATER;
+      return COMPARE_RESULT_GREATER;
     else
-      result = COMPARE_RESULT_EQUAL;
+      return COMPARE_RESULT_EQUAL;
   }
 };
 
@@ -164,65 +184,62 @@ struct Comparer<T, typename enable_if<IsVisitable<T>::value>::type>
 
   explicit Comparer(T value) : rhs(value) {}
 
-  void visitArray(const CollectionData &lhs) {
+  CompareResult visitArray(const CollectionData &lhs) {
     ArrayComparer comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitObject(const CollectionData &lhs) {
+  CompareResult visitObject(const CollectionData &lhs) {
     ObjectComparer comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitFloat(Float lhs) {
+  CompareResult visitFloat(Float lhs) {
     Comparer<Float> comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitString(const char *lhs) {
+  CompareResult visitString(const char *lhs) {
     Comparer<const char *> comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitRawJson(const char *lhsData, size_t lhsSize) {
+  CompareResult visitRawJson(const char *lhsData, size_t lhsSize) {
     RawComparer comparer(lhsData, lhsSize);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitNegativeInteger(UInt lhs) {
+  CompareResult visitNegativeInteger(UInt lhs) {
     NegativeIntegerComparer comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitPositiveInteger(UInt lhs) {
+  CompareResult visitPositiveInteger(UInt lhs) {
     Comparer<UInt> comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitBoolean(bool lhs) {
+  CompareResult visitBoolean(bool lhs) {
     Comparer<bool> comparer(lhs);
-    accept(comparer);
+    return accept(comparer);
   }
 
-  void visitNull() {
+  CompareResult visitNull() {
     NullComparer comparer;
-    accept(comparer);
+    return accept(comparer);
   }
 
  private:
   template <typename TComparer>
-  void accept(TComparer &comparer) {
-    rhs.accept(comparer);
-    switch (comparer.result) {
+  CompareResult accept(TComparer &comparer) {
+    CompareResult reversedResult = rhs.accept(comparer);
+    switch (reversedResult) {
       case COMPARE_RESULT_GREATER:
-        result = COMPARE_RESULT_LESS;
-        break;
+        return COMPARE_RESULT_LESS;
       case COMPARE_RESULT_LESS:
-        result = COMPARE_RESULT_GREATER;
-        break;
+        return COMPARE_RESULT_GREATER;
       default:
-        result = comparer.result;
-        break;
+        return reversedResult;
     }
   }
 };
@@ -230,8 +247,7 @@ struct Comparer<T, typename enable_if<IsVisitable<T>::value>::type>
 template <typename T1, typename T2>
 CompareResult compare(const T1 &lhs, const T2 &rhs) {
   Comparer<T2> comparer(rhs);
-  lhs.accept(comparer);
-  return comparer.result;
+  return lhs.accept(comparer);
 }
 
 inline int variantCompare(const VariantData *a, const VariantData *b) {

src/ArduinoJson/Variant/VariantData.hpp

@@ -34,8 +34,8 @@ class VariantData {
   // - no virtual
   // - no inheritance
 
-  template <typename Visitor>
-  void accept(Visitor &visitor) const {
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor &visitor) const {
     switch (type()) {
       case VALUE_IS_FLOAT:
         return visitor.visitFloat(_content.asFloat);

src/ArduinoJson/Variant/VariantFunctions.hpp

@@ -9,12 +9,13 @@
 
 namespace ARDUINOJSON_NAMESPACE {
 
-template <typename Visitor>
-inline void variantAccept(const VariantData *var, Visitor &visitor) {
+template <typename TVisitor>
+inline typename TVisitor::result_type variantAccept(const VariantData *var,
+                                                    TVisitor &visitor) {
   if (var != 0)
-    var->accept(visitor);
+    return var->accept(visitor);
   else
-    visitor.visitNull();
+    return visitor.visitNull();
 }
 
 inline const CollectionData *variantAsArray(const VariantData *var) {

src/ArduinoJson/Variant/VariantRef.hpp

@@ -261,9 +261,9 @@ class VariantRef : public VariantRefBase<VariantData>,
     return variantAs<T>(_data, _pool);
   }
 
-  template <typename Visitor>
-  void accept(Visitor &visitor) const {
-    variantAccept(_data, visitor);
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor &visitor) const {
+    return variantAccept(_data, visitor);
   }
 
   // Change the type of the variant
@@ -347,9 +347,9 @@ class VariantConstRef : public VariantRefBase<const VariantData>,
   VariantConstRef(const VariantData *data) : base_type(data) {}
   VariantConstRef(VariantRef var) : base_type(var._data) {}
 
-  template <typename Visitor>
-  void accept(Visitor &visitor) const {
-    variantAccept(_data, visitor);
+  template <typename TVisitor>
+  typename TVisitor::result_type accept(TVisitor &visitor) const {
+    return variantAccept(_data, visitor);
   }
 
   template <typename T>