Perhaps I am just stupid, but I can't quite grok that. What object is the predicate evaluated over, how, and at what moment?
Originally I've thought when some event causes the trigger to fire, the predicate would just be evaluated over that event; but that can't be that simple, see please details below.
I've set (in a 3rd party application; Home, far as I can say, does not allow that) a predicate “only when both of a pair of lights are off”. The predicate works perfectly, and the event really performs its action set only when both of the lights are off, so far so good.
Nevertheless, I've dumped the predicate, and it looks like this (the first line is my own dump which is a bit more concise; the 2nd one is the standard description just to make sure that my own dump works properly):
(((self.characteristic == 'Power State' of 'Lustr O') && (self.characteristicValue == 0)) && ((self.characteristic == 'Power State' of 'Knihovna') && (self.characteristicValue == 0)))
(characteristic == <HMCharacteristic, Unique ID: 2E046807-9127-565F-B9CB-10BC0F2EE6D2, Type: 00000025, Instance ID: 9> AND characteristicValue == 0) AND (characteristic == <HMCharacteristic, Unique ID: 7444CCCE-1C1B-5234-8CAE-01DA4D811B8B, Type: 00000025, Instance ID: 9> AND characteristicValue == 0)
I can't understand that at all :(
I must be missing something of great importance, but it seems to me that a predicate which can be just as well[1] written as self.characteristic==A && self.characteristic==B && (some other conditions) can't ever evaluate to YES when A and B differ (which they self-evidently do in this case).
The “to evaluate before executing the scene” of the documentation does not really help. What do I miss, can anybody explain that? Thanks!
[1] Correct me please if I am wrong, but I do believe the logical AND is both an associative and an commutative operator, which makes this re-write fully equivalent to the original.