Commit 7d993b95 authored by Robert Hensing's avatar Robert Hensing
Browse files

lib.attrsets.hasAttrByPath: Document law and laziness, and test it

parent 72bd4bbb

lib/attrsets.nix

+7 −0
Original line number Diff line number Diff line
@@ -51,12 +51,19 @@ rec { 


  /* Return if an attribute from nested attribute set exists.



     **Laws**:

      1.  ```nix

          hasAttrByPath [] x == true

          ```



     Example:

       x = { a = { b = 3; }; }

       hasAttrByPath ["a" "b"] x

       => true

       hasAttrByPath ["z" "z"] x

       => false

       hasAttrByPath [] (throw "no need")

       => true



    Type:

      hasAttrByPath :: [String] -> AttrSet -> Bool

lib/tests/misc.nix

+5 −0
Original line number Diff line number Diff line
@@ -697,6 +697,11 @@ runTests { 
    expected = false;

  };



  testHasAttrByPathNonStrict = {

    expr = hasAttrByPath [] (throw "do not use");

    expected = true;

  };



  testLongestValidPathPrefix_empty_empty = {

    expr = attrsets.longestValidPathPrefix [ ] { };

    expected = [ ];