Can I extend nixpkgs.lib or builtins with my own library function?

[con-f-use]

Say I had a custom fetcher, that I wanted to use everywhere in a flake:

  fetchPrivatePyPi= url: builtins.fetchurl (
    let
      components = builtins.match "(.*)#sha256=([a-fA-F0-9]+).*" url;
    in {
      url = "http://my-custom-pypi.org/company/" + builtins.head components;
      hash = "sha256:" + lib.last components;
    }
  );

How would I make that similarly accessible as builtins.fetchurl?

I mean, sure, I could just import a file or use an overlay or whatever, like an animal. But maybe there's a way to extend built-ins or a way to specify a "global library" for use inside a flake. There's a kinda related nixpkgs issue that Silvan already participated in.

[con-f-use]

Covered in Nix Hour #32 - nix plugins & extending lib and builtins

@infinisil, you forgot to push the files with the various solutions to ./32/. I remember you cleaning them up in the after hour chat - would be a shame if that work went unappreciated 😉 .

[infinisil]

@con-f-use Oh yeah forgot to push it! Here it is: https://github.com/tweag/nix-hour/tree/master/32 😄