Object Oriented Programming is a holy grail of modern code-writing methodologies. As everything so fundamental, it was criticised quite heavily, with different degree of details. Some say, OOP is dead, some say it’s harmful. I think, we should reconsider our understanding of this paradigm.
If we talk about objects - we think about state (a lot) and behaviour (a little) . But in all domain models we separate between «domain» and «business» logic.
Example: A human buys bananas in a grocery store. Here set of objects Bananas change ownership and location. Object Store obtains money, frees some space in a shop, and loose some bananas. Object human looses money and gets a bananas.
Question: What object should own this logic? If it’s 3 different objects, each with it’s own functions, then who should coordinate behaviour? Is it a shop who should take money from a human and change ownership of bananas? Or Human? Or Banana? Or some different different Object?
In practice, usually it’s different object, most probably StoreService.
After that we have another question - about persistence. Somebody should store it to a database (persistent storage). Should it be domain objects? In practice, it’s usually DAO layer.
And I will not dig into details - because human usually need to pack bananas in a bag and store should manage not to run out of bananas.
So, what do we have here - our objects are passive data objects, and all behaviour is in other objects, with some dependency on external resources (database).
Is it OOP ? Well, in practice, it’s what everybody calls OOP. Clearly, something is wrong.
Looking on a Store, we will not have an idea about all it’s abilities. StoreService will give us much more information.
There is one solution I know to this problem - mix-ins. You will be able to mix some resource-dependent behaviour into domain objects, without altering domain objects much. Is it OOP ?
Nice articles on a subject:
