Unverified Commit d1de5d47 authored by Luna Nova's avatar Luna Nova
Browse files

lib.lists: undeprecate crossLists 

mapCartesianProduct's output's order relies on the iteration order of the input attrset
encouraging picking non-meaningful names or arbitrary prefixed underscores if your usecase
requires a specific order.

See this thread for examples of clunkiness required to achieve a specific ordering.
https://discourse.nixos.org/t/lib-crosslists-is-deprecated-use-lib-cartesianproductofsets-instead/41824/10
parent 73d0441d

lib/lists.nix

+2 −14
Original line number Diff line number Diff line
@@ -1814,7 +1814,7 @@ rec { 
    => [ "13" "14" "23" "24" ]

    ```



    The following function call is equivalent to the one deprecated above:

    If you have an attrset already, consider mapCartesianProduct:



    ```nix

    mapCartesianProduct (x: "${toString x.a}${toString x.b}") { a = [1 2]; b = [3 4]; }
@@ -1822,19 +1822,7 @@ rec { 
    ```

    :::

  */

  crossLists = warn ''

    lib.crossLists is deprecated, use lib.mapCartesianProduct instead.



    For example, the following function call:



    nix-repl> lib.crossLists (x: y: x+y) [[1 2] [3 4]]

    [ 4 5 5 6 ]



    Can now be replaced by the following one:



    nix-repl> lib.mapCartesianProduct ({x,y}: x+y) { x = [1 2]; y = [3 4]; }

    [ 4 5 5 6 ]

  '' (f: foldl (fs: args: concatMap (f: map f args) fs) [ f ]);

  crossLists = f: foldl (fs: args: concatMap (f: map f args) fs) [ f ];



  /**

    Remove duplicate elements from the `list`. O(n^2) complexity.