CUPID – the back story
1. Watching the tech community over a really long time, please guys, don&#x27;t swing violently from &quot;A is all good!&quot; to &quot;A is all bad!&quot; It was good for something, else so many people wouldn&#x27;t have successfully used it for so long. Work more on discrimination functions and less on hyperbole please. Future generations will thank you for it.<p>2. &quot;...coupled with the way most developers conflate subtypes with subclasses...&quot; Speaking as somebody who both likes SOLID and could write this essay&#x2F;present the deck, I think there&#x27;s a lot of confusion to go around. There are a lot of guys coding classes using rules better suited for types. There are a lot of guys applying OO paradigms to functional code and vice-versa. In general, whenever we swing from one side to the other on topics, it&#x27;s a matter of definitions. There is no such thing as &quot;code&quot;. There&#x27;s &quot;thinking&#x2F;reasoning about code&quot; and there&#x27;s coding. You can&#x27;t take the human element out and reason abstractly about the end product. Whatever the end product is, it&#x27;s a result of one&#x2F;many humans pounding away on keyboards to get there.<p>3. My opinion, for what it&#x27;s worth: as OO took off, we had to come up with heuristics as to how to think about grouping code into classes, and do it in such a way that others might reasonably get to the same place ... or at least be able to look at your code and reason about how or why you did it. That&#x27;s SOLID and the rest of it. Now we&#x27;re seeing the revenge of the FP guys, and stuff like SOLID looks completely whack to them, as it should. It&#x27;s a different way of thinking about and solving problems.<p>ADD: Trying to figure out who&#x27;s right and who&#x27;s wrong is a (philosophical) nonsense question. It&#x27;s like asking &quot;which smell is plaid?&quot; Whatever answer you get is neither going to provide you with any information or help you do anything useful in the future. (Shameless plug: Just submitted an essay I wrote last week that directly addresses reasoning about types in a large app)