Add implicit conversion from JsonDocument to JsonVariant

extras/tests/JsonDocument/CMakeLists.txt

@@ -5,6 +5,7 @@
 add_executable(JsonDocumentTests
 	add.cpp
 	BasicJsonDocument.cpp
+	cast.cpp
 	compare.cpp
 	containsKey.cpp
 	createNested.cpp

extras/tests/JsonDocument/ElementProxy.cpp

@@ -219,3 +219,29 @@ TEST_CASE("ElementProxy::operator[]") {
     REQUIRE(doc.as<std::string>() == "[null,[null,null,42]]");
   }
 }
+
+TEST_CASE("ElementProxy cast to JsonVariantConst") {
+  DynamicJsonDocument doc(4096);
+  doc[0] = "world";
+
+  const ElementProxy<JsonDocument &> ep = doc[0];
+
+  JsonVariantConst var = ep;
+
+  CHECK(var.as<std::string>() == "world");
+}
+
+TEST_CASE("ElementProxy cast to JsonVariant") {
+  DynamicJsonDocument doc(4096);
+  doc[0] = "world";
+
+  ElementProxy<JsonDocument &> ep = doc[0];
+
+  JsonVariant var = ep;
+
+  CHECK(var.as<std::string>() == "world");
+
+  var.set("toto");
+
+  CHECK(doc.as<std::string>() == "[\"toto\"]");
+}

extras/tests/JsonDocument/MemberProxy.cpp

@@ -259,3 +259,29 @@ TEST_CASE("MemberProxy::operator[]") {
     REQUIRE(doc.as<std::string>() == "{\"hello\":[null,null,42]}");
   }
 }
+
+TEST_CASE("MemberProxy cast to JsonVariantConst") {
+  DynamicJsonDocument doc(4096);
+  doc["hello"] = "world";
+
+  const MemberProxy<JsonDocument &, const char *> mp = doc["hello"];
+
+  JsonVariantConst var = mp;
+
+  CHECK(var.as<std::string>() == "world");
+}
+
+TEST_CASE("MemberProxy cast to JsonVariant") {
+  DynamicJsonDocument doc(4096);
+  doc["hello"] = "world";
+
+  MemberProxy<JsonDocument &, const char *> mp = doc["hello"];
+
+  JsonVariant var = mp;
+
+  CHECK(var.as<std::string>() == "world");
+
+  var.set("toto");
+
+  CHECK(doc.as<std::string>() == "{\"hello\":\"toto\"}");
+}

extras/tests/JsonDocument/cast.cpp

@@ -0,0 +1,18 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+#include <string>
+
+TEST_CASE("Implicit cast to JsonVariant") {
+  StaticJsonDocument<128> doc;
+
+  doc["hello"] = "world";
+
+  JsonVariant var = doc;
+
+  CHECK(var.as<std::string>() == "{\"hello\":\"world\"}");
+}