attach method
Attaches a Cancellable to this token.
Before attaching to a CancellationToken, you should check if it's already been cancelled by using isCancelled.
Implementation
void attach(Cancellable cancellable) {
assert(
!isCancelled,
'Attampted to attach to a $runtimeType that has already been cancelled.\n'
'Before calling attach() you should check isCancelled.',
);
if (!isCancelled && !_attachedCancellables.contains(cancellable)) {
_attachedCancellables.add(cancellable);
}
}