Devs aren't clairvoyant so when we're making a new type we might sometimes get this wrong. But this is a fundamental issue with type systems in general and not OOP, is it not?
Most of the languages which are suggested to be superior alternatives to OOP in this thread have immutable data records and algebraic data types as core building blocks. These are very different than C-style structs, as they can provide stronger safety guarantees without a massive ream of boilerplate.
A class or method interface promises unfortunately little around essential topics like mutability, concurrency, or termination.
What OOP offers on top of modules is extendability and polymorphism.
And these two capabilities are possible to achieve in various ways.
That is the mechanism for immutability that is traditionally provided. It is easy to opt out of that protection.
Java and C# are getting records. They're a convenience but are in no way opposed or counter to OOP.
There arent many hash map methods that will actually modify the data.
Standard OOP, on the other hand, seems to encourage such behavior. So, for example, a Company object could contain a bunch of Department objects, each of which contained a bunch of Employee objects.
These people objects could also be referenced in areas outside of the company object.
If I called a company.giveFinanceDepartmentARaiseInDollars(10000) function on the Company object, it would have an unpredictable impact on the Department/Employee objects. It may also have cascading effects in other parts of the application that may not be clear.
On the other hand, if you represented this as a company hashmap, with the keys the department structs, you would have to do something like the following instead:
company["finance"].employees.forEach(x => x.salary = x.salary + 10000); company["finance"].base_salary = company["finance"].base_salary 10000
This contrived example shows some of the pros/cons. OOP allows us to hide a lot of behavior/changes, which may mean less repetitive code. OTOH, it hides a lot of behavior/changes.
More generally the issue of global mutable state and keeping your own sanity as a developer is a problem across paradigms.
My “functional” code wasn’t actually functional.
If I had written that correctly, by returning a modified copy using a map instead of modifying the strict in a loop, your example would also be covered, because the function you’re describing would not modify any of its inputs, but instead would return a new copy. And the function wouldn’t have any side effects either, so it would once again be completely clear what’s happening.
To take an obvious example, you might load a value from a database (company or employees, say), create a new value (with the higher salary, say), then write the new value to the database.
Here are some links along the same lines:
* _Aggregate Roots_ in DDD limit pointers, https://martinfowler.com/bliki/DDD_Aggregate.html * Guidance on where to mutate, _Functional core, imperative shell_, https://www.destroyallsoftware.com/screencasts/catalog/funct...
> using immutable object doesn't make all your problems go away, it makes them different
Yes, and here is a concrete example of the kind of 'different' problems you get: nested immutable structures, say `a.b.c.d`, become harder to update than simply `a.b.c.d = newValue`. The functional solution for this is 'lenses' (and other 'optics'). My favourite Kotlin framework that I use in my day job provides lenses for HTTP - URL query parameters, request and response bodies and so on - which work very well.
Where things would get silly is if you tried to make all state internal. But that's what some purist OO approaches would do for business objects.