On iOS use Dart API instead of memcpy

generator/integration-tests/part-partof/pubspec.yaml

@@ -6,6 +6,7 @@ environment:
 dependencies:
   objectbox:
   json_serializable:
+  json_annotation: "^4.3.0"
   freezed_annotation:
 
 dev_dependencies:

objectbox/lib/src/native/bindings/flatbuffers.dart

@@ -121,7 +121,9 @@ class ReaderWithCBuffer {
   void clear() => malloc.free(_bufferPtr);
 
   ByteData access(Pointer<Uint8> dataPtr, int size) {
-    if (size > _maxBuffer) {
+    // If memcpy is not available, instead of using Dart memcpy implementation,
+    // directly convert to view which is a little faster.
+    if (isMemcpyNotAvailable || size > _maxBuffer) {
       final uint8List = dataPtr.asTypedList(size);
       return ByteData.view(uint8List.buffer, uint8List.offsetInBytes, size);
     } else {

objectbox/lib/src/native/bindings/nativemem.dart

@@ -8,10 +8,34 @@ import 'dart:io';
 final _dart_memset memset =
     _stdlib.lookupFunction<_c_memset, _dart_memset>('memset');
 
+final _dart_memcpy? _memcpyNative = _lookupMemcpyOrNull();
+
+_dart_memcpy? _lookupMemcpyOrNull() {
+  try {
+    return _stdlib.lookupFunction<_c_memcpy, _dart_memcpy>('memcpy');
+  } catch (_) {
+    return null;
+  }
+}
+
+/// If the native memcpy function is not available
+/// and a Dart implementation is used.
+final isMemcpyNotAvailable = _memcpyNative == null;
+
+final _dart_memcpy _memcpyDart = (dest, src, length) {
+  dest
+      .asTypedList(length)
+      .setAll(0, src.asTypedList(length).getRange(0, length));
+};
+
 /// memcpy (destination, source, num) copies the values of num bytes from the
 /// data pointed to by source to the memory block pointed to by destination.
-final _dart_memcpy memcpy =
-    _stdlib.lookupFunction<_c_memcpy, _dart_memcpy>('memcpy');
+///
+/// Note: the native memcpy might not be available
+/// (e.g. for Flutter on iOS 15 simulator), then a Dart implementation is used
+/// to copy data via asTypedList (which is much slower).
+/// https://github.com/objectbox/objectbox-dart/issues/313
+final _dart_memcpy memcpy = _memcpyNative ?? _memcpyDart;
 
 // FFI signature
 typedef _dart_memset = void Function(Pointer<Uint8>, int, int);