[mbrodersen]

Don't until you need to. If you are planning to leave your current job then look at job offerings in the market and learn the tech needed to get one of those jobs. And since the technology underlying whatever tech is currently fashionable hasn't changed the last 50 years, it will be relatively easy to learn enough to get a job. The rest you learn on the job when solving specific problems. I would instead focus on learning the core tech that hasn't changed for 50+ years. Including functional programming, logic programming, how a computer fundamentally works (NAND gates) etc. What you learn from that will never become obsolete. You just need to translate what you learn into whatever the latest fashion framework/language call it and ignore the false hype.

[mbrodersen]

For example: people who learned lisp years ago are now laughing about the hype higher level functions (lambdas etc.) are getting. It is ancient technology. Same when Java introduced garbage collection. Yet another ancient technology. However my argument is not that you should learn lisp today to get a job. You should learn it to understand the fundamental technologies that future fashionable frameworks/languages will use. Same goes for type theory. Rust is also using ancient technology (linear types) that you would already have known about long before Rust showed up if you learned type theory. The next step after Rush is of course dependent types.