Construct and attach to a parent slot to create a new child slot.
template< typename CancellationSlot, typename Filter> constexpr cancellation_state( CancellationSlot slot, Filter filter);
The parent cancellation slot to which the state will be attached.
A function object that is used to transform incoming cancellation signals as they are received from the parent slot. This function object must have the signature:
asio::cancellation_type_t filter( asio::cancellation_type_t);
The library provides the following pre-defined cancellation filters: