Commit 0445cc8a authored by Glen Huang's avatar Glen Huang
Browse files

lib.lists.replaceElemAt: init 

It's very easy to resort to lib.take + lib.drop to accomplish this, but it's not obvious that it actually performs quite badly.

Replacing an item in a list should be a relative common operation.
parent 865f635c

lib/default.nix

+1 −0
Original line number Diff line number Diff line
@@ -295,6 +295,7 @@ let 
        elemAt

        isList

        concatAttrValues

        replaceElemAt

        ;

      inherit (self.strings)

        concatStrings

lib/lists.nix

+37 −0
Original line number Diff line number Diff line
@@ -2019,4 +2019,41 @@ rec { 
    :::

  */

  concatAttrValues = set: concatLists (attrValues set);



  /**

    Replaces a list's nth element with a new element



    # Inputs



    `list`

    : Input list



    `idx`

    : index to replace



    `newElem`

    : new element to replace with



    # Type



    ```

    replaceElemAt :: [a] -> int - b -> [a]

    ```



    # Examples

    :::{.example}

    ## `replaceElemAt` usage example



    ```nix

    lib.replaceElemAt` [1 2 3] 0 "a"

    => ["a" 2 3]

    ```



    :::

  */

  replaceElemAt =

    list: idx: newElem:

    assert lib.assertMsg (idx >= 0 && idx < length list)

      "'lists.replaceElemAt' called with index ${toString idx} on a list of size ${toString (length list)}";

    genList (i: if i == idx then newElem else elemAt list i) (length list);

}

lib/tests/misc.nix

+13 −0
Original line number Diff line number Diff line
@@ -4909,4 +4909,17 @@ runTests { 
      targetTarget = "prefix-tt";

    };

  };



  testReplaceElemAt = {

    expr = lib.replaceElemAt [ 1 2 3 ] 1 "a";

    expected = [

      1

      "a"

      3

    ];

  };



  testReplaceElemAtOutOfRange = testingThrow (lib.replaceElemAt [ 1 2 3 ] 5 "a");



  testReplaceElemAtNegative = testingThrow (lib.replaceElemAt [ 1 2 3 ] (-1) "a");

}