[Nix-dev] variable scope / recursion

[Mathijs Kwik]

On Fri, Jul 6, 2012 at 2:28 PM, Kirill Elagin <kirelagin at gmail.com> wrote:
> 2012/7/6 Mathijs Kwik <mathijs at bluescreen303.nl>
>>
>> Yeah I saw those comments too, but I can't see how that would work.
>> Because the "original" (pkgsOrig) set is built by passing pkgs (the
>> final set) to pkgsFun.
>> In other words, the set references itself, which is perfectly normal
>> in a lazy setting.
>> The notion of "original" makes sense for the attributes that get
>> overwritten, but for the rest, I would expect a "shine through".
>
>
> As Shea already pointed out there is ``__overrides`` dark magic involved.
> Basically, your overrides are never added to pkgs directly, I mean, there is
> no something like "pkgs = overrides // origPkgs".

The documentation clearly states __overrides is more powerful than //,
because // would leave the original set looking at the old values when
introspecting itself. With __overrides, they _do_ get added to the
set, and even replace the items inside, so other items in the set see
the new values.

So this __overrides magic is indeed why I would expect this to work,
as it gives a consistent attrset which can look at itself and see the
(new) consistent view.

>
> --
> Кирилл Елагин
>