Another solution is to eliminate classes and only use structs or similar plain objects. Makes mocking and testing functions much easier. At this point I see no reason for OOP whatsoever and consider it a big mistake.
The abstract concept of OOP (messages between complex objects, as defined by Alan Kay) is an attempt at mimicking biological systems. Most modern languages implement data abstraction, but call it OOP, where they encapsulate some functionality with the data it operates on. Really helped with varying data formats in the AirForce in the 60s, apparently. There isn't anything wrong with this abstract concept either - it's a way of structuring a solution, with trade-offs.
Support for unit testing and mocking has little to do with OOP, and everything to do with the underling platform. Both C++ and Java, for example, do not have a special runtime mode where arbitrary replacement of code or data could occur. This is necessary for mocking functionality that is considered implementation detail and hidden by design. The hidden part is great for production code, not great for testing.
For example, if an object in java has a field like 'private final HttpClient client = new CurlBasedHttpClient();' this code is essentially untestable because there is no way in Java to tell the JVM "during testing, when this class instantiates an HttpClient, use my MockHttpClient".
Kotlin fixed some of that with MockK, which can mock the constructor of a Kotlin object, and you can return your mock implementation when the constructor is invoked.
Clearly, it's a platform issue. There could be a world where you could replace any object in the stdlib or any method or field with a mock version. JavaScript is much more flexible in that regard, which is why unit testing js code is much easier.
The root of it all stems from the fact that unit tests need to change some implementation details of the world around the object, but production code should not be able to, in order to get all the benefits of encapsulation.
If you get rid of modern OOP, you are swinging the pendulum in the opposite direction, where your tests are easy to write on any platform, because everything is open and easily accessible, but your code will suffer from issues that creep up when structures are open and easily accessible, such as increased coupling and reduced cohesion.
I stand by my statement that OOP is totally unnecessary.
Edit: This is more blunt than I intended it to be. For what it's worth, I happen to agree with you in principle, but I also think you're taking the roof off the car here and boldly claiming that the experience is so much better in the summer. What about winter? What about when it rains? What are the trade-offs? Not mentioning the downsides means that you either haven't found them, haven't thought about them or are intentionally omitting them from the discussion.
To dismiss the whole of OOD/OOP so cavalierly just goes to show they don't know what they are talking about.
Much of the success of Modern Software is directly due to the wholesale adoption of OOD/OOP in the last few decades.
Separation of Concerns, Modularization, Reusability, Type Hierarchies, Type Composition, Interface contract-based programming, Frameworks etc. were all made mainstream by OOD/OOP. These are things taken for granted by programmers today. As somebody who has been doing OOD/OOP since the early nineties i can tell you it was the single biggest reason for the explosion of Software in the past few decades.
As a concrete example, early in my career i had programmed in C using the Windows API; both 16-bit and Win32 (Thank you Charles Petzold). It was difficult, tedious and a lot of work. And then Microsoft introduced MFC (Microsoft Foundation Classes) Framework with Visual C++ IDE. With a few clicks of the wizard, i had a complete skeleton application with a lot of hard work already done for you. That was a revelation for me on the power of OOD/OOP. Things i had slaved over in Win32 was now at the fingertips of every noob who could type. The same revelation happened (but not to the same extent) when i moved from Xlib to Motif on Unix platforms.
I had pointed you to Bertrand Meyer's book OOSC2 (in my other comment) as the book to read to understand OOD/OOP. Another great book to study is Barbara Liskov and John Guttag's Program Development in Java: Abstraction, Specification, and Object-Oriented Design.
I was formally trained and cut my teeth in OOP code bases and my latest company we are very light on classes. 99% is plain objects and modules that operate on them. Everything is very straightforward and logical. In my side projects I’ve stopped using classes as well and it’s so much cleaner.
This is opinion and preference. If I hired a guy who wanted to litter the code base with AbstractUserBeanFactoryFactories I’d have to let them go because it’s a situation I don’t want anymore.
This is putting the Cart before the Horse. Computers, Internet etc. can't do anything without the Software to drive them. That software is written in some Language/Tool using some Paradigms and Software Engineering principles. The ease of use, ease of structuring, ease of understanding etc. of these are what drives Creation, Adoption and Expansion of Computing and Devices.
>I was formally trained and cut my teeth in OOP code bases and my latest company we are very light on classes. 99% is plain objects and modules that operate on them. Everything is very straightforward and logical. In my side projects I’ve stopped using classes as well and it’s so much cleaner.
If you think merely using a syntactical structure like "class" (and Design Patterns) is what makes code OOP, then you don't understand OOP. You can do various degrees of OOP without language syntactical support. This is why i listed the principles and not some syntactic sugar in my previous comment. It is a way of thinking and Software Engineering which has given the most "bang-for-buck" so far in the Industry.
>This is opinion and preference. If I hired a guy who wanted to litter the code base with AbstractUserBeanFactoryFactories I’d have to let them go because it’s a situation I don’t want anymore.
Opinion and Preferences must be based on facts else it is only as good as "Flat Earther" category and nothing more can be discussed.
Class s: fun a(self)... fun b(self)...
The problem is mutability not how state is bound to a function.
Though it’s not always practical, like when needing to push an element to an array for making updated state. It is nevertheless possible to shave of pure parts considerably making mutability easier to maintain.
Similar, OOP is an obfuscated way to run a function with a context. The first time you separate the data in the context from an object, it’ll be hard to get it right and make it easier than to just use Objects and Methods. But once you’ve done it two or three times, it’s as easy as breathing.
You can optimize loading the context to be better than copying a bunch of unaligned data in lots of ways, but polymorphism is a common way to get there.
I am a Scala programmer, and our code mixes OO and FP. Almost all of our classes are completely immutable.
In the end, you will always need to encapsulate data and functions in some manner. The FP approach involves module systems, but as I understand it, objects in Scala actually provide a better module system than found in pure FP languages.
Using a totally non-OOP functional style, you can either instantiate state within a function or pass it in from the calling context, which is the same trade-off that dependency injection targets.
However you structure it, there will always be "glue code" that ties the nice inmutable code with the outside-interacting bits, and if you want to unit test those, dependency injection (with functions or state, not classes or instances) is still the way to go.
The few times I had to use Java afterwards I felt the same - all OOP features were unnecessary or at least didn't feel like the most straightforward approach. Nowadays I never use classes in Python, JS etc., it's just not needed - and in the case of Python it makes JSON insanely cumbersome.