What is the 100% correct way of changing Data Object class property in Magento 2?

Question

I wanted to ask this question a long time ago)
It is A very simple thing - modify any property for data object dynamically (product,category or something else).

Frankly I always used the observer class for this purpose.

But corresponding to a magento technical guidlines:

4.3. Plugins SHOULD NOT be added to data objects.
14.3. Events SHOULD NOT change a state of observable objects.

Can anybody explain how should I add timestamp, say, to the product meta_title property on the front conforming to these rules?

P.S. Please, do not suggest to change meta title in the template)
Let's assume, I need this modified meta_title in many places.

[Edited]
P.S.2 Formally the class rewrite (or reference) is a solution in this situation, but we know it is a bad practice overall and also it is too excessive to use reference to modify one property.

Answer 1

To conform to both those guidelines you are able to create a preference for the Magento\Cms\Api\Data\PageInterface via a di.xml preference which then substitutes the behaviour of getMetaTitle().

But as these are guidelines only I would rate using an after plugin more favourable to the above, ie afterGetMetaTitle().

The word observe usually implies that no action is done on what is being observed.