Refefing attrs property with dot in rec { ... }

Help
1

Hello,

In normal situaltion I could do:

  sysctl = rec {
    abc = 1;
    def = abc;
  };

But is it possible to do that when I need quote the property names?

  sysctl = rec {
    "net.ipv6.conf.all.forwarding" = 1;
    "net.ipv6.conf.default.forwarding" = "net.ipv6.conf.all.forwarding"; # will not work
  };

Thank you.

2

I do not see how to make it work with rec, but a let ... in will work.
For example:

let 
  sysctl = {
    "net.ipv6.conf.all.forwarding" = 1;
    "net.ipv6.conf.default.forwarding" = sysctl."net.ipv6.conf.all.forwarding"; 
   };
in sysctl
4 Likes
3

If this is a NixOS module, you can even do:

{ config, ... }: {
  boot.kernel.sysctl = {
    "net.ipv6.conf.all.forwarding" = 1;
    "net.ipv6.conf.default.forwarding" = config.boot.kernel.sysctl."net.ipv6.conf.all.forwarding";
  };
}

rec is generally considered an antipattern, and Iā€™m personally not fond of excessive use of let bindings either since they make things hard to override in downstream modules (and kinda awkward to read).

5 Likes
4

Thank you @markuskowa and @TLATER , I was thinking that there is some less known syntax for that.

I use it as often as I can since it makes the code shorter :wink: . Thank you.