[throwaway9870]

I find I need to learn it all because I write code that interacts with other code. I find myself reading example code that uses advanced C++ constructs, or sleuthing though a 3rd party library to understand it. Every time I find a library with a "modern C++" take on a problem (json parsing, etc.) I know I am going to have to dust off my knowledge and even learn something to make use of it. Very high cost. It is just a tough ecosystem to exist in as somebody who isn't 100% c++.

I remember starting out with Python and only knowing a subset of it, but as soon as I started writing real apps that interacted with the larger Python ecosystem, I found myself having to learn the full language (or at least a lot more than I did writing my own isolated code).

[lenkite]

All the template SNIFAE stuff hidden in highly generic libraries for is going to become quite simplified with C++ 20 concepts. Also, to be honest, it wasn't _all_ that complicated as long as you kept a few patterns in mind.