Better Async and Sync Organization

[rainyl]

• async object detect #115 (comment)

• async object detect #115 (comment)

• https://github.com/dart-lang/language/blob/main/working/0107%20-%20implicit-constructors/feature-specification.md

• Static extension methods dart-lang/language#723

[rainyl]

static or factory contructors inside extensions are not supported yet, so for now, if async constructors needed, they can only be placed inside classes.

class CLAHE extends CvStruct<cvg.CLAHE> {
  CLAHE._(cvg.CLAHEPtr ptr, [bool attach = true]) : super.fromPointer(ptr) {
    if (attach) {
      finalizer.attach(this, ptr.cast(), detach: this);
    }
  }
  factory CLAHE.empty() {
    final p = calloc<cvg.CLAHE>();
    CFFI.CLAHE_Create(p);
    return CLAHE._(p);
  }

  factory CLAHE.emptyAsync() {...}
}

However, async non-static functions can be placed in extensions:

Mat apply(Mat src, {Mat? dst}) {
    dst ??= Mat.empty();
    cvRun(() => CFFI.CLAHE_Apply(ref, src.ref, dst!.ref));
    return dst;
  }

extension CLAHEAsync on CLAHE {
  Future<Mat> applyAsync(Mat src) async =>
      cvRunAsync((callback) => CFFI.CLAHE_Apply_Async(ref, src.ref, callback), matCompleter);
}

[rainyl]

Maybe this is better:

// clahe_async.dart
import '../core/base.dart';
import '../core/mat.dart';
import '../core/size.dart';
import '../opencv.g.dart' as cvg;
import 'clahe.dart';

extension CLAHEAsync on CLAHE {
  static Future<CLAHE> createAsync([
    double clipLimit = 40,
    (int width, int height) tileGridSize = (8, 8),
  ]) async =>
      cvRunAsync(
        (callback) => CFFI.CLAHE_CreateWithParams_Async(clipLimit, tileGridSize.cvd.ref, callback),
        (c, p) => c.complete(CLAHE.fromPointer(p.cast<cvg.CLAHE>())),
      );

  Future<Mat> applyAsync(Mat src) async =>
      cvRunAsync((callback) => CFFI.CLAHE_Apply_Async(ref, src.ref, callback), matCompleter);
}

and usage:

final clahe = await cv.CLAHEAsync.createAsync();
final dst = await clahe.applyAsync(mat);
expect(dst.isEmpty, false);