{
  description = "AOC.";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    nix-filter.url = "github:numtide/nix-filter";
    rust-overlay = {
      url = "github:oxalica/rust-overlay";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs =
    {
      self,
      nixpkgs,
      rust-overlay,
      nix-filter,
      ...
    }:
    let
      # Utilities
      inherit (nixpkgs) lib;
      # Define the systems to support (all Linux systems exposed by nixpkgs)
      systems = lib.intersectLists lib.systems.flakeExposed lib.platforms.linux;
      forAllSystems = lib.genAttrs systems;
      # Create a mapping from system to corresponding nixpkgs : https://nixos.wiki/wiki/Overlays#In_a_Nix_flake
      nixpkgsFor = forAllSystems (system: (nixpkgs.legacyPackages.${system}.extend rustOverlay));
      # =========
      rustOverlay = import rust-overlay;
      rustVersion = "stable";
      rustChannel = "latest";
    in
    {
      devShells = forAllSystems (
        system:
        let
          pkgs = nixpkgsFor.${system};
          rust = pkgs.rust-bin.${rustVersion}.${rustChannel}.default.override {
            extensions = [
              "rust-src"
              "rust-analyzer"
            ];
          };
        in
        {
          default = pkgs.mkShell {
            nativeBuildInputs = (
              with pkgs;
              [
                rust
                sccache
              ]
            );

            buildInputs = [ ];

            shellHook = ''
              echo "RUST C: "$(rustc --version)" - "$(which rustc)
              export RUSTC_WRAPPER="sccache"
            '';
          };
        }
      );
    };
}