[skn0tt]

I see why you're missing an explanation on why classes should be avoided. In fact, your opinion is very similar to mine - I also think that, especially in the context of the FP-influenced React, data should be separated from behaviour - I mean how exactly are you going to preserve immutability using OOP? React just works a lot better when there's no self-mutating objects.

Could you elaborate on why you think that classes should be used when implementing controllers? I tend to think of controller classes as singletons, which kind of contradict using classes in the first place.

[mosdl]

Any method that mutates returns a copy, pretty easy to preserve immutability in OOP.

[skn0tt]

Then what do you do about the old version of the mutated object? There will still be references to it in other parts of your object model, which will now be out of date. I think that the concept of objects preserving identity is central to OOP, which simply contradicts immutability.

[pas]

Could you give a concrete example?

Why would you somehow pass objects around that are not "final"?

I mean the objects that get pinned here and there are specifically designed to serve as wrappers for some state, hence they encapsulate that state, and thus they are mutable. (For example a DB connection/manager object, a service registry, a cookie/localStorage repository.)

Where the immutability usually helps is with shuffling data around, parallel computing (concurrent access, no need to lock), etc.