Dart sealed class

main.dart

void main() {
  f(A1('1'));
  f(A2(2));
  // f(A3()); // Abstract classes cannot be instantiated
  f(A31('A3',31));
  f(A32('A3',32));
  f(A33('A3','33'));
}

void f(A x) {
  final r = switch (x) {
    A1() => 'x = ${x.x}',
    A2(:var y) => 'y = $y',
    A31(:var a, :var e) => 'super type = $e, a = $a',
    A33(:var c, :var e) => 'super type = $e, c type = ${c.runtimeType}, c = $c',
    // default for all other A3 subtypes (A32)
    A3() => 'x is some other A3 type'

  };
  print('runtime: ${x.runtimeType} unboxing: $r');
}

// root sealed class
sealed class A {}

// subtype of A
class A1 extends A {
  final String x;

  A1(this.x);
}

// another subtype of A
class A2 extends A {
  final int y;
  A2(this.y);
}

// subtype of A which is a sealed class of other subclasses
sealed class A3 extends A {
  final String e;
  A3(this.e);
}

// subtype of A3
class A31 extends A3 {
  final int a;
  A31(super.e, this.a);
}

// another subtype of A3
class A32 extends A3 {
  final int b;
  A32(super.e, this.b);
}

// subtype of A3 with generic parameter
class A33<T> extends A3 {
  final T c;
  A33(super.e, this.c);
}