Usage question: Tag change event

[intensite]

Not an issue per say, more a usage question.

Is it feasible/possible to code an event to trap when a PLC tag value changes? Some kind of a subscription system.
I would like to publish to a MQTT topic, but only if the tag value has changed.

If no built-in feature allows for this, I was planning to implement an array of "tag objects" that would hold something like
( tagName, lastValue, currentValue ) and then regularly poll & compare the currentValue with the lastValue for each tags to be monitored.

Not the most elegant. Do you have a better solution?