How would one apply command query separation (CQS), when result data is needed from a command?

Question

In wikipedia\'s definition of command query separation, it is stated that

More formally, methods should return a value only if they are referentially t

Answer 1

Well, this is a pretty old question but I post this just for the record. Whenever you use an event, you can instead use a delegate. Use events if you have many interested parties, otherwise use a delegate in a callback style:

void CreateNewOrder(Customer buyer, Product item, Action onOrderCreated)

you can also have a block for the case where the operation failed

void CreateNewOrder(Customer buyer, Product item, Action onOrderCreated, Action onOrderCreationFailed)

This decrease the cyclomatic complexity on the client code

CreateNewOrder(buyer: new Person(), item: new Product(), 
              onOrderCreated: order=> {...},
              onOrderCreationFailed: error => {...});

Hope this helps any lost soul out there...