castCallbackResult<R> static method

R castCallbackResult<R>(Object? result)

ENG-011: Safely cast a callback result to the expected type R.

This handles the case where a generic method callback may return null but the expected type R may or may not be nullable. For example, SynchronousFuture.then<R>() where R could be String (non-nullable) or String? (nullable).

Usage in generated bridge code:

return t.then((p0) {
  final result = D4.callInterpreterCallback(visitor!, fn, [p0]);
  return D4.castCallbackResult<R>(result);
});

Implementation

static R castCallbackResult<R>(Object? result) {
  if (result == null) {
    // Check if R accepts null (i.e., R is nullable like `String?`)
    // The `null is R` test returns true for nullable types.
    if (null is R) {
      return null as R;
    }
    throw ArgumentD4rtException(
      'Callback returned null but expected non-nullable type',
    );
  }
  // Attempt to cast to R - explicit cast needed for AOT
  if (result is R) {
    return result as R;
  }
  // If direct cast fails, try unwrapping bridge values
  final unwrapped = unwrapInterpreterValue(result);
  if (unwrapped is R) {
    // ignore: unnecessary_cast
    return unwrapped as R; // Explicit cast for AOT
  }
  throw ArgumentD4rtException(
    'Callback returned ${result.runtimeType}, expected $R',
  );
}