ArduinoJson 7’s Release Notes

• Make JSON_STRING_SIZE(N) return N+1 to fix third-party code (issue #2054)

• Improve error messages when using char or char* (issue #2043)
• Reduce stack consumption (issue #2046)
• Fix compatibility with GCC 4.8 (issue #2045)

• Fix assertion poolIndex < count_ after JsonDocument::clear() (issue #2034)

• Fix “no matching function” with JsonObjectConst::operator[] (issue #2019)
• Remove unused files in the PlatformIO package
• Fix volatile bool serialized as 1 or 0 instead of true or false (issue #2029)

• Remove BasicJsonDocument
• Remove StaticJsonDocument
• Add abstract Allocator class
• Merge DynamicJsonDocument with JsonDocument
• Remove JSON_ARRAY_SIZE(), JSON_OBJECT_SIZE(), and JSON_STRING_SIZE()
• Remove ARDUINOJSON_ENABLE_STRING_DEDUPLICATION (string deduplication cannot be disabled anymore)
• Remove JsonDocument::capacity()
• Store the strings in the heap
• Reference-count shared strings
• Always store serialized("string") by copy (#1915)
• Remove the zero-copy mode of deserializeJson() and deserializeMsgPack()
• Fix double lookup in to<JsonVariant>()
• Fix double call to size() in serializeMsgPack()
• Include ARDUINOJSON_SLOT_OFFSET_SIZE in the namespace name
• Remove JsonVariant::shallowCopy()
• JsonDocument’s capacity grows as needed, no need to pass it to the constructor anymore
• JsonDocument’s allocator is not monotonic anymore, removed values get recycled
• Show a link to the documentation when user passes an unsupported input type
• Remove JsonDocument::memoryUsage()
• Remove JsonDocument::garbageCollect()
• Add deserializeJson(JsonVariant, ...) and deserializeMsgPack(JsonVariant, ...) (#1226)
• Call shrinkToFit() in deserializeJson() and deserializeMsgPack()
• serializeJson() and serializeMsgPack() replace the content of std::string and String instead of appending to it
• Replace add() with add<T>() (add(T) is still supported)
• Remove createNestedArray() and createNestedObject() (use to<JsonArray>() and to<JsonObject>() instead)

BREAKING CHANGES

As every major release, ArduinoJson 7 introduces several breaking changes. I added some stubs so that most existing programs should compile, but I highty recommend you upgrade your code.

JsonDocument

In ArduinoJson 6, you could allocate the memory pool on the stack (with StaticJsonDocument) or in the heap (with DynamicJsonDocument).
In ArduinoJson 7, the memory pool is always allocated in the heap, so StaticJsonDocument and DynamicJsonDocument have been merged into JsonDocument.

In ArduinoJson 6, JsonDocument had a fixed capacity; in ArduinoJson 7, it has an elastic capacity that grows as needed. Therefore, you don’t need to specify the capacity anymore, so the macros JSON_ARRAY_SIZE(), JSON_OBJECT_SIZE(), and JSON_STRING_SIZE() have been removed.

// ArduinoJson 6
StaticJsonDocument<256> doc;
// or
DynamicJsonDocument doc(256);

// ArduinoJson 7
JsonDocument doc;

In ArduinoJson 7, JsonDocument reuses released memory, so garbageCollect() has been removed.
shrinkToFit() is still available and releases the over-allocated memory.

Due to a change in the implementation, it’s not possible to store a pointer to a variant from another JsonDocument, so shallowCopy() has been removed.

In ArduinoJson 6, the meaning of memoryUsage() was clear: it returned the number of bytes used in the memory pool.
In ArduinoJson 7, the meaning of memoryUsage() would be ambiguous, so it has been removed.

Custom allocators

In ArduinoJson 6, you could specify a custom allocator class as a template parameter of BasicJsonDocument.
In ArduinoJson 7, you must inherit from ArduinoJson::Allocator and pass a pointer to an instance of your class to the constructor of JsonDocument.

// ArduinoJson 6
class MyAllocator {
  // ...
};
BasicJsonDocument<MyAllocator> doc(256);

// ArduinoJson 7
class MyAllocator : public ArduinoJson::Allocator {
  // ...
};
MyAllocator myAllocator;
JsonDocument doc(&myAllocator);

createNestedArray() and createNestedObject()

In ArduinoJson 6, you could create a nested array or object with createNestedArray() and createNestedObject().
In ArduinoJson 7, you must use add<T>() or to<T>() instead.

For example, to create [[],{}], you would write:

// ArduinoJson 6
arr.createNestedArray();
arr.createNestedObject();

// ArduinoJson 7
arr.add<JsonArray>();
arr.add<JsonObject>();

And to create {"array":[],"object":{}}, you would write:

// ArduinoJson 6
obj.createNestedArray("array");
obj.createNestedObject("object");

// ArduinoJson 7
obj["array"].to<JsonArray>();
obj["object"].to<JsonObject>();