Added ElementProxy::getOrAddElement() (fixes #1311)

CHANGELOG.md

@@ -7,6 +7,7 @@ HEAD
 * Added comparisons (`>`, `>=`, `==`, `!=`, `<`, and `<=`) between `JsonVariant`s
 * Added string deduplication (issue #1303)
 * Fixed `copyArray()` not working with `String`, `ElementProxy`, and `MemberProxy`
+* Fixed error `getOrAddElement is not a member of ElementProxy` (issue #1311)
 
 v6.15.2 (2020-05-15)
 -------

extras/tests/ElementProxy/CMakeLists.txt

@@ -9,6 +9,7 @@ add_executable(ElementProxyTests
 	remove.cpp
 	set.cpp
 	size.cpp
+	subscript.cpp
 )
 
 add_test(ElementProxy ElementProxyTests)

extras/tests/ElementProxy/subscript.cpp

@@ -7,7 +7,7 @@
 
 using namespace ARDUINOJSON_NAMESPACE;
 
-TEST_CASE("MemberProxy::operator[]") {
+TEST_CASE("ElementProxy::operator[]") {
   DynamicJsonDocument doc(4096);
   ElementProxy<JsonDocument&> ep = doc[1];
 

src/ArduinoJson/Array/ElementProxy.hpp

@@ -135,6 +135,10 @@ class ElementProxy : public VariantOperators<ElementProxy<TArray> >,
     return getOrAddUpstreamElement().getElement(index);
   }
 
+  VariantRef getOrAddElement(size_t index) const {
+    return getOrAddUpstreamElement().getOrAddElement(index);
+  }
+
   FORCE_INLINE void remove(size_t index) const {
     getUpstreamElement().remove(index);
   }