Development shells with Nix: four quick examples

I wanted to use GoCV for one of my projects (to find and extract paper documents from within a larger scan), without permanently having OpenCV on my system. This seemed like a good example use-case to demonstrate a couple of Nix commands I like to use, covering quick interactive one-off dev shells to fully declarative, hermetic, reproducible, shareable dev shells. Notably, you don’t need to use NixOS to run these commands! You can install and use Nix on any Linux system like Debian, Arch, etc., as long as y