[devoutsalsa]

>> If you don't allow components to mutate state locally,

Code mutation is, in my personal experience, a shit show. With Elixir, you I have to worry about some random process mutating your data because it can't, as it's literally immutable. I have never, not a single time, wished I could mutate a data structure in Elixir, because I can think of no case where it makes my life easier. Even quasi-objects, in the C++/Java OOP sense, like GenServers w/ internal state may appear to be mutating data from the outside, but from the inside they still rely on copying the data to update the state. It's so much easier for me to reason about.

Maybe different things simply appeal to different people. I could make arguments for OOP being harder to scale, but maybe that's just true for how my brain works.

[applepple]

State mutations are safe and easy to handle if the state is fully contained inside a blackbox (a class) and you only return copies of the state but never the actual references.

A blackbox should never expose object references (its internal state) to its parent components. It should also avoid passing object references to child components unless it's sure that the child component will never mutate this state in an unexpected way.