Improved speed of serializeXxx() when writing to a String

extras/tests/Helpers/WString.h

@@ -9,16 +9,10 @@
 // Reproduces Arduino's String class
 class String {
  public:
-  String& operator+=(char c) {
-    _str += c;
+  String& operator+=(const char* rhs) {
+    _str += rhs;
     return *this;
   }
-  String& operator+=(int);  // no used, just to add ambiguity
-
-  unsigned char reserve(size_t capacity) {
-    _str.reserve(capacity);
-    return 1;
-  }
 
   size_t length() const {
     return _str.size();
@@ -28,12 +22,21 @@ class String {
     return _str.c_str();
   }
 
+  bool operator==(const char* s) const {
+    return _str == s;
+  }
+
+  friend std::ostream& operator<<(std::ostream& lhs, const ::String& rhs) {
+    lhs << rhs._str;
+    return lhs;
+  }
+
  private:
   std::string _str;
 };
 
 class StringSumHelper;
 
-bool operator==(const std::string& lhs, const ::String& rhs) {
+inline bool operator==(const std::string& lhs, const ::String& rhs) {
   return lhs == rhs.c_str();
 }

extras/tests/Misc/StringWriter.cpp

@@ -3,6 +3,7 @@
 // MIT License
 
 #define ARDUINOJSON_ENABLE_ARDUINO_STRING 1
+#define ARDUINOJSON_STRING_BUFFER_SIZE 5
 #include <ArduinoJson.h>
 #include <catch.hpp>
 #include "custom_string.hpp"
@@ -59,7 +60,39 @@ TEST_CASE("Writer<std::string>") {
 TEST_CASE("Writer<String>") {
   ::String output;
   Writer< ::String> sb(output);
+
   common_tests(sb, output);
+
+  SECTION("Writes characters to temporary buffer") {
+    // accumulate in buffer
+    sb.write('a');
+    sb.write('b');
+    sb.write('c');
+    REQUIRE(output == "");
+
+    // flush when full
+    sb.write('d');
+    REQUIRE(output == "abcd");
+
+    // flush on destruction
+    sb.write('e');
+    sb.~Writer();
+    REQUIRE(output == "abcde");
+  }
+
+  SECTION("Writes strings to temporary buffer") {
+    // accumulate in buffer
+    print(sb, "abc");
+    REQUIRE(output == "");
+
+    // flush when full, and continue to accumulate
+    print(sb, "de");
+    REQUIRE(output == "abcd");
+
+    // flush on destruction
+    sb.~Writer();
+    REQUIRE(output == "abcde");
+  }
 }
 
 TEST_CASE("Writer<custom_string>") {