Using nixpkgs.legacyPackages.${system} vs import

[ilkecan]

I forgot that Nix does not implement maximal laziness.

@zimbatm

if both A and B import nixpkgs { inherit system; } , there are two instances of nixpkgs instead of one.

I assumed the function call would be memoized in here but it seems that is not the case.

@zimbatm

In contrast, if both A and B access nixpkgs.legacyPackages.${system} , and that they both depend on the same nixpkgs flake, there will only be one evaluation of nixpkgs.

If I understand correctly, the difference in here is that the result is stored as an attribute value therefore it will be evaluated once.