Generic type inference bug report: working example

main.dart

enum DType<T extends num> { int64<int>(), float64<double>() }

class Tensor<DT extends DType<T>, T extends num> {
  final List<T> values;
  final DT dtype;
  final Object shape;

  const Tensor(this.values, this.dtype, this.shape);

  Tensor<DT2, T2> castSwitchedFunc<DT2 extends DType<T2>, T2 extends num>(
    DT2 dtype2,
  ) {
    final converter =
        switch (dtype2) {
              DType.int64 => (num v) => v.toInt(),
              DType.float64 => (num v) => v.toDouble(),
            }
            as T2 Function(num);
    return Tensor(values.map(converter).toList(), dtype2, shape);
  }

  Tensor<DT2, T2> castSwitchedList<DT2 extends DType<T2>, T2 extends num>(
    DT2 dtype2,
  ) {
    final vs =
        switch (dtype2) {
              DType.int64 => values.map((num v) => v.toInt()).toList(),
              DType.float64 => values.map((num v) => v.toDouble()).toList(),
            }
            as List<T2>;
    return Tensor(vs, dtype2, shape);
  }

  Tensor<DT2, T2> castSwitchedRecord<DT2 extends DType<T2>, T2 extends num>(
    DT2 dtype2,
  ) {
    final (
      vs,
      dt2,
    ) = switch (dtype2) {
          DType.int64 => (values.map((v) => v.toInt()).toList(), DType.int64),
          DType.float64 => (
            values.map((v) => v.toDouble()).toList(),
            DType.float64,
          ),
        }
        as (List<T2>, DT2);
    return Tensor(vs, dtype2, shape);
  }

  Tensor<DT2, T2> castSwitchedTensor<T2 extends num, DT2 extends DType<T2>>(
    DT2 dtype2,
  ) {
    return switch (dtype2) {
          DType.int64 => Tensor(
            values.map((v) => v.toInt()).toList(),
            DType.int64,
            shape,
          ),
          DType.float64 => Tensor(
            values.map((v) => v.toDouble()).toList(),
            DType.float64,
            shape,
          ),
        }
        as Tensor<DT2, T2>;
  }
}

void main() {
  const i64 = Tensor([0], DType.int64, 'square');
  for (final (result, name) in [
    (i64.castSwitchedFunc(DType.float64), 'castSwitchedFunc'),
    (i64.castSwitchedList(DType.float64), 'castSwitchedList'),
    (i64.castSwitchedRecord(DType.float64), 'castSwitchedRecord'),
    (i64.castSwitchedTensor(DType.float64), 'castSwitchedTensor'),
  ]) {
    if (result is Tensor<DType<double>, double>) {
      print('$name passed');
    } else {
      print('$name FAILED');
    }
  }
}