Async property query returns result too early

[Buggaboo]

If you run the branch #51 and #58, and compare the count and find result on the PropertyQuery, you'll find that the find function sometimes returns a partially correct result set, with certain random bytes (every time you run it), that are the same as the random bytes as count consistently returns.

This leads me to think that these obx functions return via ffi before the actual correct values are populated on the array alloc. This reminds me of the async await the Future discussion #49 .

[Buggaboo]

In the meantime, the users should sum, avg, etc. on Entity properties, using, higher-order dart functions on collections, e.g.:

final all = box.getAll(); // or some query
final sum = all.map((s) => s.someIntProp ?? 0).toList().reduce((a,b) => a + b); // ?? if prop is nullable
final avg  = sum / box.count();
final maxEntityOfSomeProp = all.reduce((a, b) => a.someIntProp > b.someIntProp ? a : b);
final maxOfProp = maxEntityOfSomeProp[0].someIntProp;

[vaind]

There is no async property query. The native call is synchronous, it cannot return before the data is ready.

I've found the issue causing wrong results of find() - it's a regression in OBX_id_array::items() introduced during the conversion to dart2.6. It stopped returning a copy of the list, as the comment said and returned a reference to the original list. You've used this method as a template when implementing the other obx_*_array structs, thus replicating this problem.
See 7641c85 for a fix.

Closing this issue, let's address the rest (if there are any more problems) in a property-query PR.

BTW regarding all the OBX_*_array structs - could a generic be used instead of having a copy of each? That should also reduce the amount of duplication in the caller code