Add JsonVariant::link() (resolves #1343)

extras/tests/JsonVariant/CMakeLists.txt

@@ -13,6 +13,7 @@ add_executable(JsonVariantTests
 	createNested.cpp
 	is.cpp
 	isnull.cpp
+	link.cpp
 	memoryUsage.cpp
 	misc.cpp
 	nesting.cpp

extras/tests/JsonVariant/add.cpp

@@ -43,4 +43,14 @@ TEST_CASE("JsonVariant::add()") {
 
     REQUIRE(var.as<std::string>() == "{\"val\":123}");
   }
+
+  SECTION("add to linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2.add(42);
+    var.link(doc2);
+
+    var.add(666);  // no-op
+
+    CHECK(var.as<std::string>() == "[42]");
+  }
 }

extras/tests/JsonVariant/as.cpp

@@ -267,4 +267,97 @@ TEST_CASE("JsonVariant::as()") {
 
     REQUIRE(variant.as<MY_ENUM>() == ONE);
   }
+
+  SECTION("linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    variant.link(doc2);
+
+    SECTION("as<std::string>()") {
+      CHECK(variant.as<std::string>() == "{\"hello\":\"world\"}");
+    }
+
+    SECTION("as<JsonArray>()") {
+      JsonArray a = variant.as<JsonArray>();
+      CHECK(a.isNull() == true);
+    }
+
+    SECTION("as<JsonObject>()") {
+      JsonObject o = variant.as<JsonObject>();
+      CHECK(o.isNull() == true);
+    }
+
+    SECTION("as<JsonObjectConst>()") {
+      JsonObjectConst o = variant.as<JsonObjectConst>();
+      CHECK(o.isNull() == false);
+      CHECK(o.size() == 1);
+      CHECK(o["hello"] == "world");
+    }
+  }
+
+  SECTION("linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2.add("hello");
+    doc2.add("world");
+    variant.link(doc2);
+
+    SECTION("as<std::string>()") {
+      CHECK(variant.as<std::string>() == "[\"hello\",\"world\"]");
+    }
+
+    SECTION("as<JsonArray>()") {
+      JsonArray a = variant.as<JsonArray>();
+      CHECK(a.isNull() == true);
+    }
+
+    SECTION("as<JsonArrayConst>()") {
+      JsonArrayConst a = variant.as<JsonArrayConst>();
+      CHECK(a.isNull() == false);
+      CHECK(a.size() == 2);
+      CHECK(a[0] == "hello");
+      CHECK(a[1] == "world");
+    }
+
+    SECTION("as<JsonObject>()") {
+      JsonObject o = variant.as<JsonObject>();
+      CHECK(o.isNull() == true);
+    }
+  }
+
+  SECTION("linked int") {
+    StaticJsonDocument<128> doc2;
+    doc2.set(42);
+    variant.link(doc2);
+
+    CHECK(variant.as<int>() == 42);
+    CHECK(variant.as<double>() == 42.0);
+  }
+
+  SECTION("linked double") {
+    StaticJsonDocument<128> doc2;
+    doc2.set(42.0);
+    variant.link(doc2);
+
+    CHECK(variant.as<int>() == 42);
+    CHECK(variant.as<double>() == 42.0);
+  }
+
+  SECTION("linked string") {
+    StaticJsonDocument<128> doc2;
+    doc2.set("hello");
+    variant.link(doc2);
+
+    CHECK(variant.as<std::string>() == "hello");
+  }
+
+  SECTION("linked bool") {
+    StaticJsonDocument<128> doc2;
+    variant.link(doc2);
+
+    doc2.set(true);
+    CHECK(variant.as<bool>() == true);
+
+    doc2.set(false);
+    CHECK(variant.as<bool>() == false);
+  }
 }

extras/tests/JsonVariant/clear.cpp

@@ -23,4 +23,15 @@ TEST_CASE("JsonVariant::clear()") {
 
     REQUIRE(var.isNull() == true);
   }
+
+  SECTION("doesn't alter linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    var.clear();
+
+    CHECK(var.isNull() == true);
+    CHECK(doc2.as<std::string>() == "{\"hello\":\"world\"}");
+  }
 }

extras/tests/JsonVariant/compare.cpp

@@ -34,6 +34,20 @@ TEST_CASE("Compare JsonVariant with value") {
     CHECK_FALSE(a < b);
     CHECK_FALSE(a > b);
   }
+
+  SECTION("linked 42 vs 42") {
+    StaticJsonDocument<128> doc2;
+    doc2.set(42);
+    a.link(doc2);
+    int b = 42;
+
+    CHECK(a == b);
+    CHECK(a <= b);
+    CHECK(a >= b);
+    CHECK_FALSE(a != b);
+    CHECK_FALSE(a < b);
+    CHECK_FALSE(a > b);
+  }
 }
 
 TEST_CASE("Compare JsonVariant with JsonVariant") {
@@ -313,4 +327,19 @@ TEST_CASE("Compare JsonVariant with JsonVariant") {
     CHECK_FALSE(a > b);
     CHECK_FALSE(a >= b);
   }
+
+  SECTION("linked 42 vs link 42") {
+    StaticJsonDocument<128> doc2, doc3;
+    doc2.set(42);
+    doc3.set(42);
+    a.link(doc2);
+    b.link(doc3);
+
+    CHECK(a == b);
+    CHECK(a <= b);
+    CHECK(a >= b);
+    CHECK_FALSE(a != b);
+    CHECK_FALSE(a < b);
+    CHECK_FALSE(a > b);
+  }
 }

extras/tests/JsonVariant/containsKey.cpp

@@ -12,19 +12,28 @@ TEST_CASE("JsonVariant::containsKey()") {
   DynamicJsonDocument doc(4096);
   JsonVariant var = doc.to<JsonVariant>();
 
-  SECTION("containsKey(const char*) returns true") {
+  SECTION("containsKey(const char*)") {
     var["hello"] = "world";
 
     REQUIRE(var.containsKey("hello") == true);
     REQUIRE(var.containsKey("world") == false);
   }
 
-  SECTION("containsKey(std::string) returns true") {
+  SECTION("containsKey(std::string)") {
     var["hello"] = "world";
 
     REQUIRE(var.containsKey(std::string("hello")) == true);
     REQUIRE(var.containsKey(std::string("world")) == false);
   }
+
+  SECTION("linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    CHECK(var.containsKey("hello") == true);
+    CHECK(var.containsKey("world") == false);
+  }
 }
 
 TEST_CASE("JsonVariantConst::containsKey()") {

extras/tests/JsonVariant/copy.cpp

@@ -84,6 +84,16 @@ TEST_CASE("JsonVariant::set(JsonVariant)") {
     REQUIRE(doc2.memoryUsage() == JSON_STRING_SIZE(7));
   }
 
+  SECTION("stores linked object by pointer") {
+    StaticJsonDocument<128> doc3;
+    doc3["hello"] = "world";
+    var1.link(doc3);
+    var2.set(var1);
+
+    REQUIRE(doc1.memoryUsage() == 0);
+    REQUIRE(doc2.memoryUsage() == 0);
+  }
+
   SECTION("destination is unbound") {
     JsonVariant unboundVariant;
 

extras/tests/JsonVariant/createNested.cpp

@@ -18,6 +18,17 @@ TEST_CASE("JsonVariant::createNestedObject()") {
     REQUIRE(variant[0]["value"] == 42);
     REQUIRE(obj.isNull() == false);
   }
+
+  SECTION("does nothing on linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2[0] = 42;
+    variant.link(doc2);
+
+    variant.createNestedObject();
+
+    CHECK(variant.size() == 1);
+    CHECK(variant[0] == 42);
+  }
 }
 
 TEST_CASE("JsonVariant::createNestedArray()") {
@@ -30,6 +41,17 @@ TEST_CASE("JsonVariant::createNestedArray()") {
     REQUIRE(variant.is<JsonArray>() == true);
     REQUIRE(arr.isNull() == false);
   }
+
+  SECTION("does nothing on linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2[0] = 42;
+    variant.link(doc2);
+
+    variant.createNestedArray();
+
+    CHECK(variant.size() == 1);
+    CHECK(variant[0] == 42);
+  }
 }
 
 TEST_CASE("JsonVariant::createNestedObject(key)") {
@@ -43,6 +65,17 @@ TEST_CASE("JsonVariant::createNestedObject(key)") {
     REQUIRE(variant.is<JsonObject>() == true);
     REQUIRE(variant["weather"]["temp"] == 42);
   }
+
+  SECTION("does nothing on linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    variant.link(doc2);
+
+    variant.createNestedObject("weather");
+
+    CHECK(variant.size() == 1);
+    CHECK(variant["hello"] == "world");
+  }
 }
 
 TEST_CASE("JsonVariant::createNestedArray(key)") {
@@ -55,4 +88,15 @@ TEST_CASE("JsonVariant::createNestedArray(key)") {
     REQUIRE(variant.is<JsonObject>() == true);
     REQUIRE(arr.isNull() == false);
   }
+
+  SECTION("does nothing on linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    variant.link(doc2);
+
+    variant.createNestedArray("items");
+
+    CHECK(variant.size() == 1);
+    CHECK(variant["hello"] == "world");
+  }
 }

extras/tests/JsonVariant/is.cpp

@@ -144,6 +144,24 @@ TEST_CASE("JsonVariant::is<T>()") {
     CHECK(variant.is<MYENUM2>() == false);
   }
 
+  SECTION("linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2[0] = "world";
+    variant.link(doc2);
+
+    CHECK(variant.is<JsonArray>() == false);
+    CHECK(variant.is<JsonArrayConst>() == true);
+    CHECK(variant.is<JsonVariant>() == true);
+    CHECK(variant.is<JsonVariantConst>() == true);
+    CHECK(variant.is<JsonObject>() == false);
+    CHECK(variant.is<JsonObjectConst>() == false);
+    CHECK(variant.is<int>() == false);
+    CHECK(variant.is<float>() == false);
+    CHECK(variant.is<bool>() == false);
+    CHECK(variant.is<const char *>() == false);
+    CHECK(variant.is<MYENUM2>() == false);
+  }
+
   SECTION("JsonObject") {
     variant.to<JsonObject>();
 
@@ -161,6 +179,44 @@ TEST_CASE("JsonVariant::is<T>()") {
     CHECK(variant.is<JsonVariant>() == true);
     CHECK(variant.is<JsonVariantConst>() == true);
   }
+
+  SECTION("linked object") {
+    StaticJsonDocument<1024> doc2;
+    doc2["hello"] = "world";
+    variant.link(doc2);
+
+    CHECK(variant.is<JsonObject>() == false);
+    CHECK(variant.is<JsonObjectConst>() == true);
+    CHECK(variant.is<JsonVariant>() == true);
+    CHECK(variant.is<JsonVariantConst>() == true);
+    CHECK(variant.is<JsonArray>() == false);
+    CHECK(variant.is<JsonArrayConst>() == false);
+    CHECK(variant.is<int>() == false);
+    CHECK(variant.is<float>() == false);
+    CHECK(variant.is<bool>() == false);
+    CHECK(variant.is<const char *>() == false);
+    CHECK(variant.is<MYENUM2>() == false);
+    CHECK(variant.is<JsonVariant>() == true);
+    CHECK(variant.is<JsonVariantConst>() == true);
+  }
+
+  SECTION("linked int") {
+    StaticJsonDocument<1024> doc2;
+    doc2.set(42);
+    variant.link(doc2);
+
+    CHECK(variant.is<JsonObjectConst>() == false);
+    CHECK(variant.is<JsonVariantConst>() == true);
+    CHECK(variant.is<JsonObject>() == false);
+    CHECK(variant.is<JsonVariant>() == true);
+    CHECK(variant.is<JsonArray>() == false);
+    CHECK(variant.is<JsonArrayConst>() == false);
+    CHECK(variant.is<int>() == true);
+    CHECK(variant.is<float>() == true);
+    CHECK(variant.is<bool>() == false);
+    CHECK(variant.is<const char *>() == false);
+    CHECK(variant.is<MYENUM2>() == true);
+  }
 }
 
 TEST_CASE("JsonVariantConst::is<T>()") {
@@ -316,4 +372,58 @@ TEST_CASE("JsonVariantConst::is<T>()") {
     CHECK(cvariant.is<const char *>() == false);
     CHECK(cvariant.is<MYENUM2>() == false);
   }
+
+  SECTION("linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2[0] = "world";
+    variant.link(doc2);
+
+    CHECK(cvariant.is<JsonArrayConst>() == true);
+    CHECK(cvariant.is<JsonVariantConst>() == true);
+    CHECK(cvariant.is<JsonArray>() == false);
+    CHECK(cvariant.is<JsonVariant>() == false);
+    CHECK(cvariant.is<JsonObject>() == false);
+    CHECK(cvariant.is<JsonObjectConst>() == false);
+    CHECK(cvariant.is<int>() == false);
+    CHECK(cvariant.is<float>() == false);
+    CHECK(cvariant.is<bool>() == false);
+    CHECK(cvariant.is<const char *>() == false);
+    CHECK(cvariant.is<MYENUM2>() == false);
+  }
+
+  SECTION("linked object") {
+    StaticJsonDocument<1024> doc2;
+    doc2["hello"] = "world";
+    variant.link(doc2);
+
+    CHECK(cvariant.is<JsonObjectConst>() == true);
+    CHECK(cvariant.is<JsonVariantConst>() == true);
+    CHECK(cvariant.is<JsonObject>() == false);
+    CHECK(cvariant.is<JsonVariant>() == false);
+    CHECK(cvariant.is<JsonArray>() == false);
+    CHECK(cvariant.is<JsonArrayConst>() == false);
+    CHECK(cvariant.is<int>() == false);
+    CHECK(cvariant.is<float>() == false);
+    CHECK(cvariant.is<bool>() == false);
+    CHECK(cvariant.is<const char *>() == false);
+    CHECK(cvariant.is<MYENUM2>() == false);
+  }
+
+  SECTION("linked int") {
+    StaticJsonDocument<1024> doc2;
+    doc2.set(42);
+    variant.link(doc2);
+
+    CHECK(cvariant.is<JsonObjectConst>() == false);
+    CHECK(cvariant.is<JsonVariantConst>() == true);
+    CHECK(cvariant.is<JsonObject>() == false);
+    CHECK(cvariant.is<JsonVariant>() == false);
+    CHECK(cvariant.is<JsonArray>() == false);
+    CHECK(cvariant.is<JsonArrayConst>() == false);
+    CHECK(cvariant.is<int>() == true);
+    CHECK(cvariant.is<float>() == true);
+    CHECK(cvariant.is<bool>() == false);
+    CHECK(cvariant.is<const char *>() == false);
+    CHECK(cvariant.is<MYENUM2>() == true);
+  }
 }

extras/tests/JsonVariant/isnull.cpp

@@ -9,17 +9,17 @@ TEST_CASE("JsonVariant::isNull()") {
   DynamicJsonDocument doc(4096);
   JsonVariant variant = doc.to<JsonVariant>();
 
-  SECTION("return true when Undefined") {
+  SECTION("returns true when Undefined") {
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return false when Integer") {
+  SECTION("returns false when Integer") {
     variant.set(42);
 
     REQUIRE(variant.isNull() == false);
   }
 
-  SECTION("return false when EmptyArray") {
+  SECTION("returns false when EmptyArray") {
     DynamicJsonDocument doc2(4096);
     JsonArray array = doc2.to<JsonArray>();
 
@@ -27,7 +27,7 @@ TEST_CASE("JsonVariant::isNull()") {
     REQUIRE(variant.isNull() == false);
   }
 
-  SECTION("return false when EmptyObject") {
+  SECTION("returns false when EmptyObject") {
     DynamicJsonDocument doc2(4096);
     JsonObject obj = doc2.to<JsonObject>();
 
@@ -35,41 +35,54 @@ TEST_CASE("JsonVariant::isNull()") {
     REQUIRE(variant.isNull() == false);
   }
 
-  SECTION("return true after set(JsonArray())") {
+  SECTION("returns true after set(JsonArray())") {
     variant.set(JsonArray());
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return true after set(JsonObject())") {
+  SECTION("returns true after set(JsonObject())") {
     variant.set(JsonObject());
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return false after set('hello')") {
+  SECTION("returns false after set('hello')") {
     variant.set("hello");
     REQUIRE(variant.isNull() == false);
   }
 
-  SECTION("return true after set((char*)0)") {
+  SECTION("returns true after set((char*)0)") {
     variant.set(static_cast<char*>(0));
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return true after set((const char*)0)") {
+  SECTION("returns true after set((const char*)0)") {
     variant.set(static_cast<const char*>(0));
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return true after set(serialized((char*)0))") {
+  SECTION("returns true after set(serialized((char*)0))") {
     variant.set(serialized(static_cast<char*>(0)));
     REQUIRE(variant.isNull() == true);
   }
 
-  SECTION("return true after set(serialized((const char*)0))") {
+  SECTION("returns true after set(serialized((const char*)0))") {
     variant.set(serialized(static_cast<const char*>(0)));
     REQUIRE(variant.isNull() == true);
   }
 
+  SECTION("returns true for a linked null") {
+    StaticJsonDocument<128> doc2;
+    variant.link(doc2);
+    CHECK(variant.isNull() == true);
+  }
+
+  SECTION("returns false for a linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2[0] = 42;
+    variant.link(doc2);
+    CHECK(variant.isNull() == false);
+  }
+
   SECTION("works with JsonVariantConst") {
     variant.set(42);
 

extras/tests/JsonVariant/link.cpp

@@ -0,0 +1,77 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2022, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+TEST_CASE("JsonVariant::link()") {
+  StaticJsonDocument<1024> doc1, doc2;
+  JsonVariant variant = doc1.to<JsonVariant>();
+
+  SECTION("JsonVariant::link(JsonDocument&)") {
+    doc2["hello"] = "world";
+
+    variant.link(doc2);
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"world\"}");
+    CHECK(variant.memoryUsage() == 0);
+
+    // altering the linked document should change the result
+    doc2["hello"] = "WORLD!";
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"WORLD!\"}");
+  }
+
+  SECTION("JsonVariant::link(MemberProxy)") {
+    doc2["obj"]["hello"] = "world";
+
+    variant.link(doc2["obj"]);
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"world\"}");
+    CHECK(variant.memoryUsage() == 0);
+
+    // altering the linked document should change the result
+    doc2["obj"]["hello"] = "WORLD!";
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"WORLD!\"}");
+  }
+
+  SECTION("JsonVariant::link(ElementProxy)") {
+    doc2[0]["hello"] = "world";
+
+    variant.link(doc2[0]);
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"world\"}");
+    CHECK(variant.memoryUsage() == 0);
+
+    // altering the linked document should change the result
+    doc2[0]["hello"] = "WORLD!";
+
+    CHECK(variant.as<std::string>() == "{\"hello\":\"WORLD!\"}");
+  }
+
+  SECTION("target is unbound") {
+    JsonVariant unbound;
+    variant["hello"] = "world";
+
+    variant.link(unbound);
+
+    CHECK(variant.isUnbound() == false);
+    CHECK(variant.isNull() == true);
+    CHECK(variant.memoryUsage() == 0);
+    CHECK(variant.size() == 0);
+  }
+
+  SECTION("variant is unbound") {
+    JsonVariant unbound;
+    doc2["hello"] = "world";
+
+    unbound.link(doc2);
+
+    CHECK(unbound.isUnbound() == true);
+    CHECK(unbound.isNull() == true);
+    CHECK(unbound.memoryUsage() == 0);
+    CHECK(unbound.size() == 0);
+  }
+}

extras/tests/JsonVariant/memoryUsage.cpp

@@ -38,4 +38,12 @@ TEST_CASE("JsonVariant::memoryUsage()") {
     REQUIRE(var.memoryUsage() == 6);
     REQUIRE(var.memoryUsage() == doc.memoryUsage());
   }
+
+  SECTION("ignore size of linked document") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+    CHECK(var.memoryUsage() == 0);
+    CHECK(var.memoryUsage() == doc.memoryUsage());
+  }
 }

extras/tests/JsonVariant/nesting.cpp

@@ -28,4 +28,12 @@ TEST_CASE("JsonVariant::nesting()") {
     var.to<JsonArray>();
     REQUIRE(var.nesting() == 1);
   }
+
+  SECTION("returns depth of linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2[0][0] = 42;
+    var.link(doc2);
+
+    CHECK(var.nesting() == 2);
+  }
 }

extras/tests/JsonVariant/or.cpp

@@ -156,4 +156,12 @@ TEST_CASE("JsonVariant::operator|()") {
     int result = variant | 42;
     REQUIRE(result == 42);
   }
+
+  SECTION("linked int | int") {
+    StaticJsonDocument<128> doc2;
+    doc2.set(42);
+    variant.link(doc2);
+    int result = variant | 666;
+    CHECK(result == 42);
+  }
 }

extras/tests/JsonVariant/remove.cpp

@@ -39,4 +39,24 @@ TEST_CASE("JsonVariant::remove()") {
 
     REQUIRE(var.as<std::string>() == "{\"a\":1}");
   }
+
+  SECTION("linked array") {
+    StaticJsonDocument<128> doc2;
+    doc2[0] = 42;
+    var.link(doc2);
+
+    var.remove(0);
+
+    CHECK(var.as<std::string>() == "[42]");
+  }
+
+  SECTION("linked object") {
+    StaticJsonDocument<128> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    var.remove("hello");
+
+    CHECK(var.as<std::string>() == "{\"hello\":\"world\"}");
+  }
 }

extras/tests/JsonVariant/size.cpp

@@ -41,4 +41,13 @@ TEST_CASE("JsonVariant::size()") {
 
     CHECK(variant.size() == 1);
   }
+
+  SECTION("linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2.add(1);
+    doc2.add(2);
+    variant.link(doc2);
+
+    CHECK(variant.size() == 2);
+  }
 }

extras/tests/JsonVariant/subscript.cpp

@@ -129,6 +129,44 @@ TEST_CASE("JsonVariant::operator[]") {
     REQUIRE(std::string("world") == variant[vla]);
   }
 #endif
+
+  SECTION("get value from linked object") {
+    StaticJsonDocument<1024> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    CHECK(var["hello"].as<std::string>() == "world");
+  }
+
+  SECTION("set value to linked object") {
+    StaticJsonDocument<1024> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    var["tutu"] = "toto";  // no-op
+
+    CHECK(doc.as<std::string>() == "{\"hello\":\"world\"}");
+    CHECK(doc2.as<std::string>() == "{\"hello\":\"world\"}");
+  }
+
+  SECTION("get value from linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2.add(42);
+    var.link(doc2);
+
+    CHECK(var[0].as<int>() == 42);
+  }
+
+  SECTION("set value to linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2.add(42);
+    var.link(doc2);
+
+    var[0] = 666;  // no-op
+
+    CHECK(doc.as<std::string>() == "[42]");
+    CHECK(doc2.as<std::string>() == "[42]");
+  }
 }
 
 TEST_CASE("JsonVariantConst::operator[]") {
@@ -201,4 +239,20 @@ TEST_CASE("JsonVariantConst::operator[]") {
     REQUIRE(var.is<JsonObject>() == false);
     REQUIRE(value == 0);
   }
+
+  SECTION("get value from linked object") {
+    StaticJsonDocument<1024> doc2;
+    doc2["hello"] = "world";
+    var.link(doc2);
+
+    CHECK(cvar["hello"].as<std::string>() == "world");
+  }
+
+  SECTION("get value from linked array") {
+    StaticJsonDocument<1024> doc2;
+    doc2.add(42);
+    var.link(doc2);
+
+    CHECK(cvar[0].as<int>() == 42);
+  }
 }