Commit 7e07b3ec authored by adisbladis's avatar adisbladis
Browse files

lib.attrsets.hasAttrByPath: Don't allocate one extra list per lookup recursion 

Using `tail` in a recursive loop like this needlessly allocates.
This changes the loop to look up by list index instead.
parent 627af21e

lib/attrsets.nix

+10 −6
Original line number Diff line number Diff line
@@ -58,13 +58,17 @@ rec { 
    attrPath:

    # The nested attribute set to check

    e:

    let attr = head attrPath;

    let

      lenAttrPath = length attrPath;

      hasAttrByPath' = n: s: let

        attr = elemAt attrPath n;

      in (

        if n == lenAttrPath then true

        else if s ? ${attr} then hasAttrByPath' (n + 1) s.${attr}

        else false

      );

    in

      if attrPath == [] then true

      else if e ? ${attr}

      then hasAttrByPath (tail attrPath) e.${attr}

      else false;



      hasAttrByPath' 0 e;



  /* Create a new attribute set with `value` set at the nested attribute location specified in `attrPath`.