[garethrowlands]

It has a fair bit to do with tooling. For example, C++ suffers from the fragile base class problem and some changes can cause long compile times. Nowadays, we have tests and deployment pipelines that are explicitly designed to let us make and deploy changes safely.

Honestly, if you cannot change your code, you have a problem.

[chillacy]

The OCP is imo poorly named, but it has far bigger implications than the post acknowledges. For one, it implies the concept of abstraction layers. In particular, base libraries should provide abstractions at the level of the library. In this way it's able to achieve being "closed for modification but open for extension".

https://drive.google.com/file/d/0BwhCYaYDn8EgN2M5MTkwM2EtNWF...

Flipping it around, if base libraries were to be always open for modification instead of extension, then instead of writing your feature logic in your own codebase, you might be tempted to submit a pull request to React.js to add your feature logic. That sounds ridiculous but that's the equivalent of what I see a lot of new engineers do when they try to fit the feature logic they need to implement anywhere it makes sense, often in some shared library in the same codebase.