Only use Dart implementation of memcpy if it is not available.

Author: greenrobot-team

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

@@ -8,13 +8,20 @@ import 'dart:io';
 final _dart_memset memset =
     _stdlib.lookupFunction<_c_memset, _dart_memset>('memset');
 
-/// If the native memcpy function should not be used.
-///
-/// memcpy is not available to Flutter on iOS 15 simulator,
-/// so use Dart API to copy data via asTypedList (which is much slower but works).
-///
-/// https://github.com/objectbox/objectbox-dart/issues/313
-final isMemcpyNotAvailable = Platform.isIOS;
+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)
@@ -23,9 +30,12 @@ final _dart_memcpy _memcpyDart = (dest, src, 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 = isMemcpyNotAvailable
-    ? _memcpyDart
-    : _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);