core/pkgs/by-name/ic/icu/packages.nix

{ ... }:
res: pkgs: super:

with pkgs; {
  icu-versions = callPackages ./. { };
  inherit (icu-versions)
    icu58 icu60 icu63 icu64 icu66 icu67 icu68 icu69 icu70 icu71 icu72 icu73
    icu74;

  icu = icu73;
}