PHP Best Practice: Using Mixed return types

Question

I understand that this topic was briefly approached here but I hope to understand the general do's and don'ts of using multiple return types in PHP. There seems to be varied opinions about this feature of PHP.

I would tend to agree that, as pointed out in the thread linked above, for errors, using exceptions is probably more suited; But, what about a function returning, say, two types of meaningful values? For example, let's say a function that returns all the lights that are OFF in a house (:) yes, I'm winging it!)

Essentially, this is what I want to convey: If a basic condition is not met and I don't see a point in going forward and computing my list, I return a boolean. Otherwise, go ahead and do so:

    public function getLightsThatAreOff($house) 
    {
        // if $house itself does not have any power, return true 
        // else 
              //compile an array of lights that are off and return then
    }

I would think that the use case mentioned above is a sort of a sweet-spot for multiple return types. In either case, I would appreciate it if someone provides a general set of guidelines on how to determine whether to use this feature or not.

Thanks!

Answer 1

Mixed types are not good, even if documented well. For example, if a method is returning an array, but there is nothing to return, then it should be an empty array, not false or anything else. i.e.

array()