Thread by @_Codito_

💡Value Object: what's that?

Basically, it's a simple object representation of some kind of reusable data structure. Unlike entity, it does not have identity, so value objects are considered as equal if underlying data is equal.

Want to know more? Read below 👇🧵 #architecture

Value Objects encapsulate data and ensure its validity - constructor can, and should, check if provided primitive values are correct. Thanks to that, when you pass VO to other methods, you can be sure it carries proper information 🙂

Value Object's reusability doesn't mean you reuse data it carries. You reuse its structure across other Value Objects or Entities. Name can be used for modelling Employee, Client and other.

So you can have several John Doe employees with the same Name, but different Id 🙂

How do you name attributes, methods, if you use private attributes with getters or public, readonly attributes does not matter. What matters is that you should model self-contained, reusable structure that carries data which is always valid for further usage.

Since Value Object is a domain concept, you should mostly use your own models & do not allow 3rd party code to leak into your domain. But in reality you probably don't want to model things that are already done.

So you can use vendor code (or infrastructure, like PHP's), but do it knowingly and with care. Don't populate your domain code with unnecessary dependencies without real added value 😊

This thread is inspired by @PovilasKorop's tweet, which IMHO provides very misleading example of Value Object. Not only `(new FullName('John Doe'))->fullName()` looks weird, but also idea of using external VOs for this is not good.

https://twitter.com/PovilasKorop/status/1598568150446080000

Let me know if you enjoyed this little thread and tell me how do you use Value Objects in your code 😎 I would happily discuss it!