Added support for custom writer classes (closes #1088)

src/ArduinoJson/Serialization/DynamicStringWriter.hpp

@@ -4,7 +4,9 @@
 
 #pragma once
 
+#include <ArduinoJson/Configuration.hpp>
 #include <ArduinoJson/Polyfills/type_traits.hpp>
+#include <ArduinoJson/Serialization/WriterSelector.hpp>
 
 #if ARDUINOJSON_ENABLE_ARDUINO_STRING
 #include <WString.h>
@@ -79,4 +81,11 @@ class DynamicStringWriter<std::basic_string<char, TCharTraits, TAllocator> > {
   string_type *_str;
 };
 #endif
+
+template <typename TDestination>
+struct WriterSelector<
+    TDestination,
+    typename enable_if<IsWriteableString<TDestination>::value>::type> {
+  typedef DynamicStringWriter<TDestination> writer_type;
+};
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/PrintWriter.hpp

@@ -0,0 +1,37 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2019
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Polyfills/type_traits.hpp>
+#include <ArduinoJson/Serialization/WriterSelector.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+class PrintWriter {
+ public:
+  explicit PrintWriter(Print& print) : _print(print) {}
+
+  size_t write(uint8_t c) {
+    return _print.write(c);
+  }
+
+  size_t write(const uint8_t* s, size_t n) {
+    return _print.write(s, n);
+  }
+
+ private:
+  // cannot be assigned
+  PrintWriter& operator=(const PrintWriter&);
+
+  Print& _print;
+};
+
+template <typename TDestination>
+struct WriterSelector<
+    TDestination,
+    typename enable_if<is_base_of<Print, TDestination>::value>::type> {
+  typedef PrintWriter writer_type;
+};
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/StreamWriter.hpp

@@ -5,8 +5,7 @@
 #pragma once
 
 #include <ArduinoJson/Configuration.hpp>
-
-#if ARDUINOJSON_ENABLE_STD_STREAM
+#include <ArduinoJson/Serialization/WriterSelector.hpp>
 
 #include <ostream>
 
@@ -33,6 +32,11 @@ class StreamWriter {
 
   std::ostream& _os;
 };
-}  // namespace ARDUINOJSON_NAMESPACE
 
-#endif  // ARDUINOJSON_ENABLE_STD_STREAM
+template <typename TDestination>
+struct WriterSelector<
+    TDestination,
+    typename enable_if<is_base_of<std::ostream, TDestination>::value>::type> {
+  typedef StreamWriter writer_type;
+};
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/WriterSelector.hpp

@@ -0,0 +1,17 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2019
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Namespace.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+
+template <typename TDestination, typename Enable = void>
+struct WriterSelector {
+  // by default, assume destination implements the Writer concept
+  typedef TDestination& writer_type;
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Serialization/serialize.hpp

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <ArduinoJson/Configuration.hpp>
 #include <ArduinoJson/Serialization/DynamicStringWriter.hpp>
 #include <ArduinoJson/Serialization/StaticStringWriter.hpp>
 
@@ -11,30 +12,26 @@
 #include <ArduinoJson/Serialization/StreamWriter.hpp>
 #endif
 
+#if ARDUINOJSON_ENABLE_ARDUINO_PRINT
+#include <ArduinoJson/Serialization/PrintWriter.hpp>
+#endif
+
 namespace ARDUINOJSON_NAMESPACE {
 
 template <template <typename> class TSerializer, typename TSource,
-          typename TDestination>
-size_t doSerialize(const TSource &source, TDestination &destination) {
-  TSerializer<TDestination> serializer(destination);
+          typename TWriter>
+size_t doSerialize(const TSource &source, TWriter &writer) {
+  TSerializer<TWriter> serializer(writer);
   source.accept(serializer);
   return serializer.bytesWritten();
 }
 
-#if ARDUINOJSON_ENABLE_STD_STREAM
-template <template <typename> class TSerializer, typename TSource>
-size_t serialize(const TSource &source, std::ostream &destination) {
-  StreamWriter writer(destination);
+template <template <typename> class TSerializer, typename TSource,
+          typename TDestination>
+size_t serialize(const TSource &source, TDestination &destination) {
+  typename WriterSelector<TDestination>::writer_type writer(destination);
   return doSerialize<TSerializer>(source, writer);
 }
-#endif
-
-#if ARDUINOJSON_ENABLE_ARDUINO_PRINT
-template <template <typename> class TSerializer, typename TSource>
-size_t serialize(const TSource &source, Print &destination) {
-  return doSerialize<TSerializer>(source, destination);
-}
-#endif
 
 template <template <typename> class TSerializer, typename TSource>
 size_t serialize(const TSource &source, char *buffer, size_t bufferSize) {
@@ -48,12 +45,4 @@ size_t serialize(const TSource &source, char (&buffer)[N]) {
   return doSerialize<TSerializer>(source, writer);
 }
 
-template <template <typename> class TSerializer, typename TSource,
-          typename TString>
-typename enable_if<IsWriteableString<TString>::value, size_t>::type serialize(
-    const TSource &source, TString &str) {
-  DynamicStringWriter<TString> writer(str);
-  return doSerialize<TSerializer>(source, writer);
-}
-
 }  // namespace ARDUINOJSON_NAMESPACE