On 28/05/17 13:18, Sergiu Ivanov wrote:
> Hello,
>
> I found myself in the need of a function which would take a list of
> Nix attribute sets and concatenate them to produce one big attribute
> set:
>
> nix-repl> concatAttrs [ {x=1;} {y=2;} ]
> {x=1; y=2;}
>
> I did quite some research online and in nixpkgs source tree and found
> a lot of cool functions, but nothing resembling to concatAttrs.
>
> Does such a function exist?
>
>
> In the meantime, I ended up writing the following definition:
>
> concatAttrs = attrList: pkgs.lib.fold (x: y: x // y) {} attrList;
>
> Do you see any isssues with such an implementation?
>
Looks like a sensible way to do it to me, though I'd be surprised if it
doesn't already exist in nixpkgs.
Do keep in mind that // is not commutative — the order matters when the
two sets contain the same key — but other than that I don't see any
issues. You might also want to look at the merging logic used for nixos
modules (lib/modules.nix), although that's significantly more complex.
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