> I like to say that immutability is a really good idea in the 1990s, especially considering how counterculture it would have been at the time. I don't mean that as diminutive or patronizing, I'm serious. It was a good cutting edge idea.

> However, nobody had any experience with it. Now we do.

Working intimately with C++ in the '90s, immutability as a concept was neither considered counterculture nor without significant experience employing it. At that time and in C++, it was commonly known as "const correctness" and was a key code review topic.

Go back another decade or two when K&R C ruled the land and that's a different story ;-).