Commit 544a1d37 authored by adisbladis's avatar adisbladis
Browse files

lib.attrsets.attrByPath: 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 7e07b3ec

lib/attrsets.nix

+21 −11
Original line number Diff line number Diff line
@@ -34,12 +34,20 @@ rec { 
    default:

    # The nested attribute set to select values from

    set:

    let attr = head attrPath;

    let

      lenAttrPath = length attrPath;

      attrByPath' = n: s: (

        if n == lenAttrPath then s

        else (

          let

            attr = elemAt attrPath n;

          in

      if attrPath == [] then set

      else if set ? ${attr}

      then attrByPath (tail attrPath) default set.${attr}

      else default;

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

          else default

        )

      );

    in

      attrByPath' 0 set;



  /* Return if an attribute from nested attribute set exists.
@@ -60,12 +68,14 @@ rec { 
    e:

    let

      lenAttrPath = length attrPath;

      hasAttrByPath' = n: s: let

      hasAttrByPath' = n: s: (

        n == lenAttrPath || (

          let

            attr = elemAt attrPath n;

      in (

        if n == lenAttrPath then true

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

          in

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

          else false

        )

      );

    in

      hasAttrByPath' 0 e;