Add as<JsonString>()

CHANGELOG.md

@@ -8,6 +8,7 @@ HEAD
   Dependent settings (like `ARDUINOJSON_DEFAULT_NESTING_LIMIT`) must be set individually.
 * Change the default of `ARDUINOJSON_USE_DOUBLE` to `1`
 * Change the default of `ARDUINOJSON_USE_LONG_LONG` to `1` on 32-bit platforms
+* Add `as<JsonString>()`
 
 v6.18.5 (2021-09-28)
 -------

extras/tests/JsonVariant/as.cpp

@@ -24,6 +24,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(0.0f == variant.as<float>());
     REQUIRE(0 == variant.as<const char*>());
     REQUIRE("null" == variant.as<std::string>());
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(4.2)") {
@@ -34,6 +35,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<std::string>() == "4.2");
     REQUIRE(variant.as<long>() == 4L);
     REQUIRE(variant.as<unsigned>() == 4U);
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(0.0)") {
@@ -41,6 +43,7 @@ TEST_CASE("JsonVariant::as()") {
 
     REQUIRE(variant.as<bool>() == false);
     REQUIRE(variant.as<long>() == 0L);
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(false)") {
@@ -50,6 +53,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == 0.0);
     REQUIRE(variant.as<long>() == 0L);
     REQUIRE(variant.as<std::string>() == "false");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(true)") {
@@ -59,6 +63,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == 1.0);
     REQUIRE(variant.as<long>() == 1L);
     REQUIRE(variant.as<std::string>() == "true");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(42)") {
@@ -69,6 +74,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<int>() == 42);
     REQUIRE(variant.as<unsigned int>() == 42U);  // issue #1601
     REQUIRE(variant.as<std::string>() == "42");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(42L)") {
@@ -77,6 +83,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<bool>() == true);
     REQUIRE(variant.as<double>() == 42.0);
     REQUIRE(variant.as<std::string>() == "42");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(-42L)") {
@@ -84,6 +91,7 @@ TEST_CASE("JsonVariant::as()") {
 
     REQUIRE(variant.as<double>() == -42.0);
     REQUIRE(variant.as<std::string>() == "-42");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(42UL)") {
@@ -92,6 +100,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<bool>() == true);
     REQUIRE(variant.as<double>() == 42.0);
     REQUIRE(variant.as<std::string>() == "42");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(0L)") {
@@ -100,6 +109,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<bool>() == false);
     REQUIRE(variant.as<double>() == 0.0);
     REQUIRE(variant.as<std::string>() == "0");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(0UL)") {
@@ -108,6 +118,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<bool>() == false);
     REQUIRE(variant.as<double>() == 0.0);
     REQUIRE(variant.as<std::string>() == "0");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(null)") {
@@ -117,12 +128,14 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == 0.0);
     REQUIRE(variant.as<long>() == 0L);
     REQUIRE(variant.as<std::string>() == "null");
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(\"42\")") {
     variant.set("42");
 
     REQUIRE(variant.as<long>() == 42L);
+    REQUIRE(variant.as<JsonString>() == "42");
   }
 
   SECTION("set(\"hello\")") {
@@ -133,6 +146,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<const char*>() == std::string("hello"));
     REQUIRE(variant.as<const char*>() == std::string("hello"));
     REQUIRE(variant.as<std::string>() == std::string("hello"));
+    REQUIRE(variant.as<JsonString>() == "hello");
   }
 
   SECTION("set(std::string(\"4.2\"))") {
@@ -143,6 +157,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == 4.2);
     REQUIRE(variant.as<const char*>() == std::string("4.2"));
     REQUIRE(variant.as<std::string>() == std::string("4.2"));
+    REQUIRE(variant.as<JsonString>() == "4.2");
   }
 
   SECTION("set(\"true\")") {
@@ -150,6 +165,7 @@ TEST_CASE("JsonVariant::as()") {
 
     REQUIRE(variant.as<bool>() == true);
     REQUIRE(variant.as<int>() == 0);
+    REQUIRE(variant.as<JsonString>() == "true");
   }
 
   SECTION("set(-1e300)") {
@@ -159,6 +175,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == -1e300);
     REQUIRE(variant.as<float>() < 0);
     REQUIRE(my::isinf(variant.as<float>()));
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(1e300)") {
@@ -168,6 +185,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<double>() == 1e300);
     REQUIRE(variant.as<float>() > 0);
     REQUIRE(my::isinf(variant.as<float>()));
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("set(1e-300)") {
@@ -176,6 +194,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<bool>() == true);
     REQUIRE(variant.as<double>() == 1e-300);
     REQUIRE(variant.as<float>() == 0);
+    REQUIRE(variant.as<JsonString>().isNull());
   }
 
   SECTION("to<JsonObject>()") {

src/ArduinoJson/Variant/ConverterImpl.hpp

@@ -129,6 +129,18 @@ struct Converter<const char*> {
   }
 };
 
+template <>
+struct Converter<String> {
+  static void toJson(String src, VariantRef dst) {
+    variantSetString(getData(dst), adaptString(src), getPool(dst));
+  }
+
+  static String fromJson(VariantConstRef src) {
+    const VariantData* data = getData(src);
+    return data ? String(data->asString(), false) : 0;
+  }
+};
+
 template <typename T>
 inline typename enable_if<IsString<T>::value, bool>::type convertToJson(
     const T& src, VariantRef dst) {