John Carmack on mutable variables

> Making almost every variable const at initialization is good practice. I wish it was the default, and mutable was a keyword.

It's funny how functional programming is slowly becoming the best practice for modern code (pure functions, no side-effects), yet functional programming languages are still considered fringe tech for some reason.

If you want a language where const is the default and mutable is a keyword, try F# for starters. I switched and never looked back.

Pure functional works great until it doesn't. For a lot of systems-y and performance-oriented code you need the escape hatches or you'll be in for a lot of pain and annoyance.

As a practical observation, I think it was easier to close this gap by adding substantial functional capabilities to imperative languages than the other way around. Historically, functional language communities were much more precious about the purity of their functional-ness than imperative languages were about their imperative-ness.