Change string copy policy: only string literal are stored by pointer

CHANGELOG.md

@@ -6,6 +6,7 @@ HEAD
 
 * Fix support for NUL characters in `deserializeJson()`
 * Make `ElementProxy` and `MemberProxy` non-copyable
+* Change string copy policy: only string literal are stored by pointer
 
 > ### BREAKING CHANGES
 >

extras/tests/JsonArray/add.cpp

@@ -17,31 +17,112 @@ TEST_CASE("JsonArray::add(T)") {
 
   SECTION("int") {
     array.add(123);
+
     REQUIRE(123 == array[0].as<int>());
     REQUIRE(array[0].is<int>());
     REQUIRE(array[0].is<double>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
   }
 
   SECTION("double") {
     array.add(123.45);
+
     REQUIRE(123.45 == array[0].as<double>());
     REQUIRE(array[0].is<double>());
     REQUIRE_FALSE(array[0].is<bool>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
   }
 
   SECTION("bool") {
     array.add(true);
-    REQUIRE(true == array[0].as<bool>());
+
+    REQUIRE(array[0].as<bool>() == true);
     REQUIRE(array[0].is<bool>());
     REQUIRE_FALSE(array[0].is<int>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
+  }
+
+  SECTION("string literal") {
+    array.add("hello");
+
+    REQUIRE(array[0].as<std::string>() == "hello");
+    REQUIRE(array[0].is<const char*>());
+    REQUIRE(array[0].is<int>() == false);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
+  }
+
+  SECTION("std::string") {
+    array.add("hello"_s);
+
+    REQUIRE(array[0].as<std::string>() == "hello");
+    REQUIRE(array[0].is<const char*>() == true);
+    REQUIRE(array[0].is<int>() == false);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
   }
 
   SECTION("const char*") {
     const char* str = "hello";
     array.add(str);
-    REQUIRE(str == array[0].as<std::string>());
+
-    REQUIRE(array[0].is<const char*>());
+    REQUIRE(array[0].as<std::string>() == "hello");
-    REQUIRE_FALSE(array[0].is<int>());
+    REQUIRE(array[0].as<const char*>() != str);
+    REQUIRE(array[0].is<const char*>() == true);
+    REQUIRE(array[0].is<int>() == false);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+
+  SECTION("serialized(const char*)") {
+    array.add(serialized("{}"));
+
+    REQUIRE(doc.as<std::string>() == "[{}]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("{}")),
+                         });
+  }
+
+  SECTION("serialized(char*)") {
+    array.add(serialized(const_cast<char*>("{}")));
+
+    REQUIRE(doc.as<std::string>() == "[{}]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("{}")),
+                         });
+  }
+
+  SECTION("serialized(std::string)") {
+    array.add(serialized("{}"_s));
+
+    REQUIRE(doc.as<std::string>() == "[{}]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("{}")),
+                         });
+  }
+
+  SECTION("serialized(std::string)") {
+    array.add(serialized("\0XX"_s));
+
+    REQUIRE(doc.as<std::string>() == "[\0XX]"_s);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString(" XX")),
+                         });
   }
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
@@ -52,7 +133,12 @@ TEST_CASE("JsonArray::add(T)") {
 
     array.add(vla);
 
-    REQUIRE("world"_s == array[0]);
+    strcpy(vla, "hello");
+    REQUIRE(array[0] == "world"_s);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
   }
 #endif
 
@@ -99,61 +185,6 @@ TEST_CASE("JsonArray::add(T)") {
 
     REQUIRE(str == array[0]);
   }
-
-  SECTION("should not duplicate const char*") {
-    array.add("world");
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                         });
-  }
-
-  SECTION("should duplicate char*") {
-    array.add(const_cast<char*>("world"));
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("world")),
-                         });
-  }
-
-  SECTION("should duplicate std::string") {
-    array.add("world"_s);
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("world")),
-                         });
-  }
-
-  SECTION("should duplicate serialized(const char*)") {
-    array.add(serialized("{}"));
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("{}")),
-                         });
-  }
-
-  SECTION("should duplicate serialized(char*)") {
-    array.add(serialized(const_cast<char*>("{}")));
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("{}")),
-                         });
-  }
-
-  SECTION("should duplicate serialized(std::string)") {
-    array.add(serialized("{}"_s));
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("{}")),
-                         });
-  }
-
-  SECTION("should duplicate serialized(std::string)") {
-    array.add(serialized("\0XX"_s));
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString(" XX")),
-                         });
-  }
 }
 
 TEST_CASE("JsonArray::add<T>()") {

extras/tests/JsonArray/subscript.cpp

@@ -59,15 +59,56 @@ TEST_CASE("JsonArray::operator[]") {
     REQUIRE(false == array[0].is<int>());
   }
 
-  SECTION("const char*") {
+  SECTION("string literal") {
-    const char* str = "hello";
+    array[0] = "hello";
 
-    array[0] = str;
+    REQUIRE(array[0].as<std::string>() == "hello");
-    REQUIRE(str == array[0].as<const char*>());
     REQUIRE(true == array[0].is<const char*>());
     REQUIRE(false == array[0].is<int>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
   }
 
+  SECTION("const char*") {
+    const char* str = "hello";
+    array[0] = str;
+
+    REQUIRE(array[0].as<std::string>() == "hello");
+    REQUIRE(true == array[0].is<const char*>());
+    REQUIRE(false == array[0].is<int>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
+  }
+
+  SECTION("std::string") {
+    array[0] = "hello"_s;
+
+    REQUIRE(array[0].as<std::string>() == "hello");
+    REQUIRE(true == array[0].is<const char*>());
+    REQUIRE(false == array[0].is<int>());
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
+  }
+
+#ifdef HAS_VARIABLE_LENGTH_ARRAY
+  SECTION("VLA") {
+    size_t i = 16;
+    char vla[i];
+    strcpy(vla, "world");
+
+    array.add("hello");
+    array[0] = vla;
+
+    REQUIRE(array[0] == "world"_s);
+  }
+#endif
+
   SECTION("nested array") {
     JsonDocument doc2;
     JsonArray arr2 = doc2.to<JsonArray>();
@@ -114,58 +155,11 @@ TEST_CASE("JsonArray::operator[]") {
     REQUIRE(str == array[0]);
   }
 
-  SECTION("should not duplicate const char*") {
-    array[0] = "world";
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                         });
-  }
-
-  SECTION("should duplicate char*") {
-    array[0] = const_cast<char*>("world");
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("world")),
-                         });
-  }
-
-  SECTION("should duplicate std::string") {
-    array[0] = "world"_s;
-    REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
-                             Allocate(sizeofString("world")),
-                         });
-  }
-
   SECTION("array[0].to<JsonObject>()") {
     JsonObject obj = array[0].to<JsonObject>();
     REQUIRE(obj.isNull() == false);
   }
 
-#ifdef HAS_VARIABLE_LENGTH_ARRAY
-  SECTION("set(VLA)") {
-    size_t i = 16;
-    char vla[i];
-    strcpy(vla, "world");
-
-    array.add("hello");
-    array[0].set(vla);
-
-    REQUIRE("world"_s == array[0]);
-  }
-
-  SECTION("operator=(VLA)") {
-    size_t i = 16;
-    char vla[i];
-    strcpy(vla, "world");
-
-    array.add("hello");
-    array[0] = vla;
-
-    REQUIRE("world"_s == array[0]);
-  }
-#endif
-
   SECTION("Use a JsonVariant as index") {
     array[0] = 1;
     array[1] = 2;

extras/tests/JsonDocument/ElementProxy.cpp

@@ -5,37 +5,60 @@
 #include <ArduinoJson.h>
 #include <catch.hpp>
 
+#include "Allocators.hpp"
 #include "Literals.hpp"
 
 using ElementProxy = ArduinoJson::detail::ElementProxy<JsonDocument&>;
 
 TEST_CASE("ElementProxy::add()") {
-  JsonDocument doc;
+  SpyingAllocator spy;
+  JsonDocument doc(&spy);
   doc.add<JsonVariant>();
   const ElementProxy& ep = doc[0];
 
-  SECTION("add(int)") {
+  SECTION("integer") {
     ep.add(42);
 
     REQUIRE(doc.as<std::string>() == "[[42]]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
   }
 
-  SECTION("add(const char*)") {
+  SECTION("string literal") {
     ep.add("world");
 
     REQUIRE(doc.as<std::string>() == "[[\"world\"]]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
   }
 
-  SECTION("add(char[])") {
+  SECTION("const char*") {
+    const char* s = "world";
+    ep.add(s);
+
+    REQUIRE(doc.as<std::string>() == "[[\"world\"]]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
+  }
+
+  SECTION("char[]") {
     char s[] = "world";
     ep.add(s);
     strcpy(s, "!!!!!");
 
     REQUIRE(doc.as<std::string>() == "[[\"world\"]]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
   }
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
-  SECTION("set(vla)") {
+  SECTION("VLA") {
     size_t i = 8;
     char vla[i];
     strcpy(vla, "world");
@@ -43,6 +66,10 @@ TEST_CASE("ElementProxy::add()") {
     ep.add(vla);
 
     REQUIRE(doc.as<std::string>() == "[[\"world\"]]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
   }
 #endif
 }

extras/tests/JsonDocument/MemberProxy.cpp

@@ -15,23 +15,53 @@ using ArduinoJson::detail::sizeofArray;
 using ArduinoJson::detail::sizeofObject;
 
 TEST_CASE("MemberProxy::add()") {
-  JsonDocument doc;
+  SpyingAllocator spy;
+  JsonDocument doc(&spy);
   const auto& mp = doc["hello"];
 
-  SECTION("add(int)") {
+  SECTION("integer") {
     mp.add(42);
 
     REQUIRE(doc.as<std::string>() == "{\"hello\":[42]}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
   }
 
-  SECTION("add(const char*)") {
+  SECTION("string literal") {
     mp.add("world");
 
     REQUIRE(doc.as<std::string>() == "{\"hello\":[\"world\"]}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
+  }
+
+  SECTION("const char*") {
+    const char* temp = "world";
+    mp.add(temp);
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":[\"world\"]}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
+  }
+
+  SECTION("char[]") {
+    char temp[] = "world";
+    mp.add(temp);
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":[\"world\"]}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+
+                         });
   }
 
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
-  SECTION("add(vla)") {
+  SECTION("VLA") {
     size_t i = 16;
     char vla[i];
     strcpy(vla, "world");
@@ -39,6 +69,10 @@ TEST_CASE("MemberProxy::add()") {
     mp.add(vla);
 
     REQUIRE(doc.as<std::string>() == "{\"hello\":[\"world\"]}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("world")),
+                         });
   }
 #endif
 }

extras/tests/JsonDocument/add.cpp

@@ -26,7 +26,7 @@ TEST_CASE("JsonDocument::add(T)") {
                          });
   }
 
-  SECTION("const char*") {
+  SECTION("string literal") {
     doc.add("hello");
 
     REQUIRE(doc.as<std::string>() == "[\"hello\"]");
@@ -35,6 +35,17 @@ TEST_CASE("JsonDocument::add(T)") {
                          });
   }
 
+  SECTION("const char*") {
+    const char* value = "hello";
+    doc.add(value);
+
+    REQUIRE(doc.as<std::string>() == "[\"hello\"]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+
   SECTION("std::string") {
     doc.add("example"_s);
     doc.add("example"_s);

extras/tests/JsonDocument/remove.cpp

@@ -20,11 +20,21 @@ TEST_CASE("JsonDocument::remove()") {
     REQUIRE(doc.as<std::string>() == "[1,3]");
   }
 
+  SECTION("string literal") {
+    doc["a"] = 1;
+    doc["a\0b"_s] = 2;
+    doc["b"] = 3;
+
+    doc.remove("a\0b");
+
+    REQUIRE(doc.as<std::string>() == "{\"a\":1,\"b\":3}");
+  }
+
   SECTION("remove(const char *)") {
     doc["a"] = 1;
     doc["b"] = 2;
 
-    doc.remove("a");
+    doc.remove(static_cast<const char*>("a"));
 
     REQUIRE(doc.as<std::string>() == "{\"b\":2}");
   }

extras/tests/JsonDocument/set.cpp

@@ -11,6 +11,21 @@ TEST_CASE("JsonDocument::set()") {
   SpyingAllocator spy;
   JsonDocument doc(&spy);
 
+  SECTION("nullptr") {
+    doc.set(nullptr);
+
+    REQUIRE(doc.isNull());
+    REQUIRE(spy.log() == AllocatorLog{});
+  }
+
+  SECTION("integer&") {
+    int toto = 42;
+    doc.set(toto);
+
+    REQUIRE(doc.as<std::string>() == "42");
+    REQUIRE(spy.log() == AllocatorLog{});
+  }
+
   SECTION("integer") {
     doc.set(42);
 
@@ -18,13 +33,23 @@ TEST_CASE("JsonDocument::set()") {
     REQUIRE(spy.log() == AllocatorLog{});
   }
 
-  SECTION("const char*") {
+  SECTION("string literal") {
     doc.set("example");
 
     REQUIRE(doc.as<const char*>() == "example"_s);
     REQUIRE(spy.log() == AllocatorLog{});
   }
 
+  SECTION("const char*") {
+    const char* value = "example";
+    doc.set(value);
+
+    REQUIRE(doc.as<const char*>() == "example"_s);
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofString("example")),
+                         });
+  }
+
   SECTION("std::string") {
     doc.set("example"_s);
 

extras/tests/JsonDocument/subscript.cpp

@@ -5,6 +5,7 @@
 #include <ArduinoJson.h>
 #include <catch.hpp>
 
+#include "Allocators.hpp"
 #include "Literals.hpp"
 
 TEST_CASE("JsonDocument::operator[]") {
@@ -16,8 +17,16 @@ TEST_CASE("JsonDocument::operator[]") {
     doc["abc\0d"_s] = "ABCD";
 
     SECTION("const char*") {
+      const char* key = "abc";
+      REQUIRE(doc[key] == "ABC");
+      REQUIRE(cdoc[key] == "ABC");
+    }
+
+    SECTION("string literal") {
       REQUIRE(doc["abc"] == "ABC");
       REQUIRE(cdoc["abc"] == "ABC");
+      REQUIRE(doc["abc\0d"] == "ABCD");
+      REQUIRE(cdoc["abc\0d"] == "ABCD");
     }
 
     SECTION("std::string") {
@@ -94,3 +103,65 @@ TEST_CASE("JsonDocument automatically promotes to array") {
 
   REQUIRE(doc.as<std::string>() == "[null,null,2]");
 }
+
+TEST_CASE("JsonDocument::operator[] key storage") {
+  SpyingAllocator spy;
+  JsonDocument doc(&spy);
+
+  SECTION("string literal") {
+    doc["hello"] = 0;
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":0}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                         });
+  }
+
+  SECTION("const char*") {
+    const char* key = "hello";
+    doc[key] = 0;
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":0}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+
+  SECTION("char[]") {
+    char key[] = "hello";
+    doc[key] = 0;
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":0}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+
+  SECTION("std::string") {
+    doc["hello"_s] = 0;
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":0}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+#if defined(HAS_VARIABLE_LENGTH_ARRAY) && \
+    !defined(SUBSCRIPT_CONFLICTS_WITH_BUILTIN_OPERATOR)
+  SECTION("VLA") {
+    size_t i = 16;
+    char vla[i];
+    strcpy(vla, "hello");
+
+    doc[vla] = 0;
+
+    REQUIRE(doc.as<std::string>() == "{\"hello\":0}");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                         });
+  }
+#endif
+}

extras/tests/JsonVariant/set.cpp

@@ -17,6 +17,15 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
   JsonDocument doc(&spy);
   JsonVariant variant = doc.to<JsonVariant>();
 
+  SECTION("string literal") {
+    bool result = variant.set("hello\0world");
+
+    REQUIRE(result == true);
+    CHECK(variant ==
+          "hello"_s);  // linked string cannot contain '\0' at the moment
+    CHECK(spy.log() == AllocatorLog{});
+  }
+
   SECTION("const char*") {
     char str[16];
 
@@ -25,8 +34,10 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
     strcpy(str, "world");
 
     REQUIRE(result == true);
-    REQUIRE(variant == "world");  // stores by pointer
+    REQUIRE(variant == "hello");  // stores by copy
-    REQUIRE(spy.log() == AllocatorLog{});
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofString("hello")),
+                         });
   }
 
   SECTION("(const char*)0") {
@@ -34,6 +45,7 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
 
     REQUIRE(result == true);
     REQUIRE(variant.isNull());
+    REQUIRE(variant.as<const char*>() == nullptr);
     REQUIRE(spy.log() == AllocatorLog{});
   }
 
@@ -105,16 +117,14 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
 #endif
 
   SECTION("std::string") {
-    std::string str;
+    std::string str = "hello\0world"_s;
-
-    str = "hello";
     bool result = variant.set(str);
     str.replace(0, 5, "world");
 
     REQUIRE(result == true);
-    REQUIRE(variant == "hello");  // stores by copy
+    REQUIRE(variant == "hello\0world"_s);  // stores by copy
     REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofString("hello")),
+                             Allocate(sizeofString("hello?world")),
                          });
   }
 

extras/tests/JsonVariant/types.cpp

@@ -7,14 +7,8 @@
 #include <catch.hpp>
 #include <limits>
 
-template <typename T>
+#include "Allocators.hpp"
-void checkValue(T expected) {
+#include "Literals.hpp"
-  JsonDocument doc;
-  JsonVariant variant = doc.to<JsonVariant>();
-
-  variant.set(expected);
-  REQUIRE(expected == variant.as<T>());
-}
 
 template <typename T>
 void checkReference(T& expected) {
@@ -39,27 +33,29 @@ void checkNumericType() {
 }
 
 TEST_CASE("JsonVariant set()/get()") {
+  SpyingAllocator spy;
+  JsonDocument doc(&spy);
+  JsonVariant variant = doc.to<JsonVariant>();
+
 #if ARDUINOJSON_USE_LONG_LONG
   SECTION("SizeOfJsonInteger") {
     REQUIRE(8 == sizeof(JsonInteger));
   }
 #endif
 
-  SECTION("Null") {
+  // /!\ Most test were moved to `JsonVariant/set.cpp`
-    checkValue<const char*>(NULL);
+  // TODO: move the remaining tests too
-  }
-  SECTION("const char*") {
-    checkValue<const char*>("hello");
-  }
-  SECTION("std::string") {
-    checkValue<std::string>("hello");
-  }
 
   SECTION("False") {
-    checkValue<bool>(false);
+    variant.set(false);
+    REQUIRE(variant.as<bool>() == false);
+    REQUIRE(spy.log() == AllocatorLog{});
   }
+
   SECTION("True") {
-    checkValue<bool>(true);
+    variant.set(true);
+    REQUIRE(variant.as<bool>() == true);
+    REQUIRE(spy.log() == AllocatorLog{});
   }
 
   SECTION("Double") {
@@ -129,10 +125,12 @@ TEST_CASE("JsonVariant set()/get()") {
 #endif
 
   SECTION("CanStoreObject") {
-    JsonDocument doc;
+    JsonDocument doc2;
-    JsonObject object = doc.to<JsonObject>();
+    JsonObject object = doc2.to<JsonObject>();
 
-    checkValue<JsonObject>(object);
+    variant.set(object);
+    REQUIRE(variant.is<JsonObject>());
+    REQUIRE(variant.as<JsonObject>() == object);
   }
 }
 

extras/tests/JsonVariantConst/subscript.cpp

@@ -54,13 +54,22 @@ TEST_CASE("JsonVariantConst::operator[]") {
     object["abc"_s] = "ABC";
     object["abc\0d"_s] = "ABCD";
 
-    SECTION("supports const char*") {
+    SECTION("string literal") {
       REQUIRE(var["ab"] == "AB"_s);
       REQUIRE(var["abc"] == "ABC"_s);
+      REQUIRE(var["abc\0d"] == "ABCD"_s);
       REQUIRE(var["def"].isNull());
       REQUIRE(var[0].isNull());
     }
 
+    SECTION("const char*") {
+      REQUIRE(var[static_cast<const char*>("ab")] == "AB"_s);
+      REQUIRE(var[static_cast<const char*>("abc")] == "ABC"_s);
+      REQUIRE(var[static_cast<const char*>("abc\0d")] == "ABC"_s);
+      REQUIRE(var[static_cast<const char*>("def")].isNull());
+      REQUIRE(var[static_cast<const char*>(0)].isNull());
+    }
+
     SECTION("supports std::string") {
       REQUIRE(var["ab"_s] == "AB"_s);
       REQUIRE(var["abc"_s] == "ABC"_s);

extras/tests/Misc/StringAdapters.cpp

@@ -16,20 +16,29 @@ using ArduinoJson::JsonString;
 using namespace ArduinoJson::detail;
 
 TEST_CASE("adaptString()") {
+  SECTION("string literal") {
+    auto s = adaptString("bravo\0alpha");
+
+    CHECK(s.isNull() == false);
+    CHECK(s.size() == 11);
+    CHECK(s.isLinked() == true);
+  }
+
   SECTION("null const char*") {
     auto s = adaptString(static_cast<const char*>(0));
 
     CHECK(s.isNull() == true);
     CHECK(s.size() == 0);
-    CHECK(s.isLinked() == true);
   }
 
   SECTION("non-null const char*") {
-    auto s = adaptString("bravo");
+    const char* p = "bravo";
+    auto s = adaptString(p);
 
     CHECK(s.isNull() == false);
     CHECK(s.size() == 5);
-    CHECK(s.isLinked() == true);
+    CHECK(s.isLinked() == false);
+    CHECK(s.data() == p);
   }
 
   SECTION("null const char* + size") {

extras/tests/MsgPackSerializer/serializeVariant.cpp

@@ -139,7 +139,8 @@ TEST_CASE("serialize MsgPack value") {
 
   SECTION("str 32") {
     std::string shortest(65536, '?');
-    checkVariant(shortest.c_str(), "\xDB\x00\x01\x00\x00"_s + shortest);
+    checkVariant(JsonString(shortest.c_str(), true),  // force store by pointer
+                 "\xDB\x00\x01\x00\x00"_s + shortest);
   }
 
   SECTION("serialized(const char*)") {

src/ArduinoJson/Array/JsonArray.hpp

@@ -66,7 +66,8 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
 
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonarray/add/
-  template <typename T>
+  template <typename T,
+            typename = detail::enable_if_t<!detail::is_const<T>::value>>
   bool add(T* value) const {
     return detail::ArrayData::addValue(data_, value, resources_);
   }

src/ArduinoJson/Document/JsonDocument.hpp

@@ -144,7 +144,8 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Replaces the root with the specified value.
   // https://arduinojson.org/v7/api/jsondocument/set/
-  template <typename TChar>
+  template <typename TChar,
+            typename = detail::enable_if_t<!detail::is_const<TChar>::value>>
   bool set(TChar* src) {
     return to<JsonVariant>().set(src);
   }
@@ -197,7 +198,7 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   // https://arduinojson.org/v7/api/jsondocument/subscript/
   template <typename TChar>
   detail::enable_if_t<
-      detail::IsString<TChar*>::value,
+      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
       detail::MemberProxy<JsonDocument&, detail::AdaptedString<TChar*>>>
   operator[](TChar* key) {
     return {*this, detail::adaptString(key)};
@@ -215,7 +216,9 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   // Gets a root object's member.
   // https://arduinojson.org/v7/api/jsondocument/subscript/
   template <typename TChar>
-  detail::enable_if_t<detail::IsString<TChar*>::value, JsonVariantConst>
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
+                          !detail::is_const<TChar>::value,
+                      JsonVariantConst>
   operator[](TChar* key) const {
     return JsonVariantConst(
         data_.getMember(detail::adaptString(key), &resources_), &resources_);
@@ -273,7 +276,8 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
 
   // Appends a value to the root array.
   // https://arduinojson.org/v7/api/jsondocument/add/
-  template <typename TChar>
+  template <typename TChar,
+            typename = detail::enable_if_t<!detail::is_const<TChar>::value>>
   bool add(TChar* value) {
     return data_.addValue(value, &resources_);
   }
@@ -289,7 +293,9 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
   // Removes a member of the root object.
   // https://arduinojson.org/v7/api/jsondocument/remove/
   template <typename TChar>
-  detail::enable_if_t<detail::IsString<TChar*>::value> remove(TChar* key) {
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
+                      !detail::is_const<TChar>::value>
+  remove(TChar* key) {
     detail::VariantData::removeMember(getData(), detail::adaptString(key),
                                       getResourceManager());
   }

src/ArduinoJson/Object/JsonObject.hpp

@@ -113,7 +113,7 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
   // https://arduinojson.org/v7/api/jsonobject/subscript/
   template <typename TChar>
   detail::enable_if_t<
-      detail::IsString<TChar*>::value,
+      detail::IsString<TChar*>::value && !detail::is_const<TChar>::value,
       detail::MemberProxy<JsonObject, detail::AdaptedString<TChar*>>>
   operator[](TChar* key) const {
     return {*this, detail::adaptString(key)};
@@ -175,8 +175,9 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
   // https://arduinojson.org/v7/api/jsonobject/containskey/
   template <typename TChar>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TChar*>::value, bool> containsKey(
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
-      TChar* key) const {
+                          !detail::is_const<TChar>::value,
+                      bool> containsKey(TChar* key) const {
     return detail::ObjectData::getMember(data_, detail::adaptString(key),
                                          resources_) != 0;
   }

src/ArduinoJson/Object/JsonObjectConst.hpp

@@ -109,7 +109,9 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
   // Gets the member with specified key.
   // https://arduinojson.org/v7/api/jsonobjectconst/subscript/
   template <typename TChar>
-  detail::enable_if_t<detail::IsString<TChar*>::value, JsonVariantConst>
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
+                          !detail::is_const<TChar>::value,
+                      JsonVariantConst>
   operator[](TChar* key) const {
     return JsonVariantConst(detail::ObjectData::getMember(
                                 data_, detail::adaptString(key), resources_),

src/ArduinoJson/Object/MemberProxy.hpp

@@ -39,7 +39,7 @@ class MemberProxy
     return *this;
   }
 
-  template <typename T>
+  template <typename T, typename = enable_if_t<!is_const<T>::value>>
   MemberProxy& operator=(T* src) {
     this->set(src);
     return *this;

src/ArduinoJson/Strings/Adapters/RamString.hpp

@@ -76,6 +76,15 @@ struct StringAdapter<TChar*, enable_if_t<IsChar<TChar>::value>> {
   }
 };
 
+template <size_t N>
+struct StringAdapter<const char (&)[N]> {
+  using AdaptedString = RamString;
+
+  static AdaptedString adapt(const char (&p)[N]) {
+    return RamString(p, N - 1, true);
+  }
+};
+
 template <typename TChar, size_t N>
 struct StringAdapter<TChar[N], enable_if_t<IsChar<TChar>::value>> {
   using AdaptedString = RamString;
@@ -86,15 +95,6 @@ struct StringAdapter<TChar[N], enable_if_t<IsChar<TChar>::value>> {
   }
 };
 
-template <>
-struct StringAdapter<const char*, void> {
-  using AdaptedString = RamString;
-
-  static AdaptedString adapt(const char* p) {
-    return AdaptedString(p, p ? ::strlen(p) : 0, true);
-  }
-};
-
 template <typename TChar>
 struct SizedStringAdapter<TChar*, enable_if_t<IsChar<TChar>::value>> {
   using AdaptedString = RamString;

src/ArduinoJson/Strings/IsString.hpp

@@ -13,7 +13,7 @@ template <typename T, typename Enable = void>
 struct IsString : false_type {};
 
 template <typename T>
-struct IsString<T, void_t<typename StringAdapter<T>::AdaptedString>>
+struct IsString<T, void_t<typename StringAdapterFor<T>::AdaptedString>>
     : true_type {};
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Strings/StringAdapter.hpp

@@ -4,8 +4,17 @@
 
 #pragma once
 
+#include <ArduinoJson/Polyfills/utility.hpp>
+
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
+// a meta function that tells if the type is a string literal (const char[N])
+template <typename T>
+struct IsStringLiteral : false_type {};
+
+template <size_t N>
+struct IsStringLiteral<const char (&)[N]> : true_type {};
+
 template <typename TString, typename Enable = void>
 struct StringAdapter;
 
@@ -13,18 +22,25 @@ template <typename TString, typename Enable = void>
 struct SizedStringAdapter;
 
 template <typename TString>
-typename StringAdapter<TString>::AdaptedString adaptString(const TString& s) {
+using StringAdapterFor =
-  return StringAdapter<TString>::adapt(s);
+    StringAdapter<conditional_t<IsStringLiteral<TString>::value, TString,
+                                remove_cv_t<remove_reference_t<TString>>>>;
+
+template <typename T>
+using AdaptedString = typename StringAdapterFor<T>::AdaptedString;
+
+template <typename TString>
+AdaptedString<TString> adaptString(TString&& s) {
+  return StringAdapterFor<TString>::adapt(detail::forward<TString>(s));
 }
 
-template <typename TChar>
+template <typename TChar, typename = enable_if_t<!is_const<TChar>::value>>
-typename StringAdapter<TChar*>::AdaptedString adaptString(TChar* p) {
+AdaptedString<TChar*> adaptString(TChar* p) {
   return StringAdapter<TChar*>::adapt(p);
 }
 
 template <typename TChar>
-typename SizedStringAdapter<TChar*>::AdaptedString adaptString(TChar* p,
+AdaptedString<TChar*> adaptString(TChar* p, size_t n) {
-                                                               size_t n) {
   return SizedStringAdapter<TChar*>::adapt(p, n);
 }
 

src/ArduinoJson/Strings/StringAdapters.hpp

@@ -70,8 +70,4 @@ static void stringGetChars(TAdaptedString s, char* p, size_t n) {
   }
 }
 
-template <typename T>
-using AdaptedString =
-    typename StringAdapter<remove_reference_t<T>>::AdaptedString;
-
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Variant/ConverterImpl.hpp

@@ -31,7 +31,7 @@ struct Converter {
     // clang-format on
   }
 
-  static T fromJson(JsonVariantConst src) {
+  static detail::decay_t<T> fromJson(JsonVariantConst src) {
     static_assert(!detail::is_same<T, char*>::value,
                   "type 'char*' is not supported, use 'const char*' instead");
 

src/ArduinoJson/Variant/JsonVariantConst.hpp

@@ -120,7 +120,9 @@ class JsonVariantConst : public detail::VariantTag,
   // Gets object's member with specified key.
   // https://arduinojson.org/v7/api/jsonvariantconst/subscript/
   template <typename TChar>
-  detail::enable_if_t<detail::IsString<TChar*>::value, JsonVariantConst>
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
+                          !detail::is_const<TChar>::value,
+                      JsonVariantConst>
   operator[](TChar* key) const {
     return JsonVariantConst(detail::VariantData::getMember(
                                 data_, detail::adaptString(key), resources_),
@@ -153,8 +155,9 @@ class JsonVariantConst : public detail::VariantTag,
   // https://arduinojson.org/v7/api/jsonvariantconst/containskey/
   template <typename TChar>
   ARDUINOJSON_DEPRECATED("use obj[\"key\"].is<T>() instead")
-  detail::enable_if_t<detail::IsString<TChar*>::value, bool> containsKey(
+  detail::enable_if_t<detail::IsString<TChar*>::value &&
-      TChar* key) const {
+                          !detail::is_const<TChar>::value,
+                      bool> containsKey(TChar* key) const {
     return detail::VariantData::getMember(getData(), detail::adaptString(key),
                                           resources_) != 0;
   }

src/ArduinoJson/Variant/VariantRefBase.hpp

@@ -77,12 +77,15 @@ class VariantRefBase : public VariantTag {
   // https://arduinojson.org/v7/api/jsonvariant/set/
   template <typename T>
   bool set(const T& value) const {
-    return doSet<Converter<remove_cv_t<T>>>(value);
+    using TypeForConverter = conditional_t<IsStringLiteral<T>::value, T,
+                                           remove_cv_t<remove_reference_t<T>>>;
+    return doSet<Converter<TypeForConverter>>(value);
   }
 
   // Copies the specified value.
   // https://arduinojson.org/v7/api/jsonvariant/set/
-  template <typename T>
+  template <typename T,
+            typename = detail::enable_if_t<!detail::is_const<T>::value>>
   bool set(T* value) const {
     return doSet<Converter<T*>>(value);
   }
@@ -123,7 +126,7 @@ class VariantRefBase : public VariantTag {
 
   // Appends a value to the array.
   // https://arduinojson.org/v7/api/jsonvariant/add/
-  template <typename T>
+  template <typename T, typename = enable_if_t<!is_const<T>::value>>
   bool add(T* value) const {
     return detail::VariantData::addValue(getOrCreateData(), value,
                                          getResourceManager());
@@ -195,7 +198,7 @@ class VariantRefBase : public VariantTag {
   // Gets or sets an object member.
   // https://arduinojson.org/v7/api/jsonvariant/subscript/
   template <typename TChar>
-  FORCE_INLINE enable_if_t<IsString<TChar*>::value,
+  FORCE_INLINE enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
                            MemberProxy<TDerived, AdaptedString<TChar*>>>
   operator[](TChar* key) const;
 

src/ArduinoJson/Variant/VariantRefBaseImpl.hpp

@@ -124,7 +124,7 @@ inline ElementProxy<TDerived> VariantRefBase<TDerived>::operator[](
 
 template <typename TDerived>
 template <typename TChar>
-inline enable_if_t<IsString<TChar*>::value,
+inline enable_if_t<IsString<TChar*>::value && !is_const<TChar>::value,
                    MemberProxy<TDerived, AdaptedString<TChar*>>>
 VariantRefBase<TDerived>::operator[](TChar* key) const {
   return {derived(), adaptString(key)};