SelectClause
Each select clause is specified with:
the object of this clause, such as the channel instance for SendChannel.onSend;
the function that specifies how this clause should be registered in the object above;
the function that modifies the internal result (passed via SelectInstance.trySelect or SelectInstance.selectInRegistrationPhase) to the argument of the user-specified block.
the function that specifies how the internal result provided via SelectInstance.trySelect or SelectInstance.selectInRegistrationPhase should be processed in case of this
select
cancellation while dispatching.