resolve method

Resolvable<T> resolve(Resolvable<T> resolvable)

Safely resolves the completer with the outcome of a Resolvable.

If the completer is already completed or is in the process of completing, this method will return an Err and have no effect.

Implementation

Resolvable<T> resolve(Resolvable<T> resolvable) {
  if (_isCompleting) {
    return Sync.err(Err('SafeCompleter<$T> is already resolving!'));
  }
  // Check terminal state directly (do NOT read `isCompleted` here — that
  // now includes the `_isCompleting` flag we're about to set below, which
  // would always make this check trip).
  if (_completer.isCompleted || _value.isSome()) {
    return Sync.err(Err('SafeCompleter<$T> is already completed!'));
  }
  _isCompleting = true;

  // `ifOk` and `ifErr` are used to handle the two possible outcomes of the
  // resolvable, ensuring the completer is correctly handled in both cases.
  return resolvable.ifOk((_, ok) {
    final okValue = ok.unwrap();
    _value = Some(okValue);
    _completer.complete(okValue);
  }).ifErr((_, err) {
    _completer.completeError(err);
  }).whenComplete((_) {
    // Ensure the lock is always released.
    _isCompleting = false;
    return resolvable;
  });
}