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

I like the event driven architecture suggestions other people have given, but I just want to throw in another point of view. Maybe you need to look at why you're actually returning data from your command. Do you actually need the result out of it, or could you get away with throwing an exception if it fails?

I'm not saying this as a universal solution, but switching to a stronger "exception on failure" instead of "send back a response" model helped me a lot in making the separation actually work in my own code. Of course, then you end up having to write a lot more exception handlers, so it's a trade off... But it's at least another angle to consider.