Flake Utils and project templates

What is flake-utils?#

Flake outputs often require the same attribute sets to be defined repeatedly for different architectures, such as x86_64-linux and aarch64-linux, making the code very verbose. flake-utils provides a simple helper function to eliminate this repetition.

1. The traditional approach

You need to iterate over all architectures manually.

{
  outputs = { self, nixpkgs }: {
    packages.x86_64-linux.default = ...;
    packages.aarch64-linux.default = ...;
  };
}

2. A concise approach with flake-utils

{
  inputs.flake-utils.url = "github:numtide/flake-utils";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system}; in
      {
        packages.default = pkgs.hello;
        devShells.default = pkgs.mkShell { buildInputs = [ pkgs.git ]; };
      }
    );
}

• eachDefaultSystem: generates outputs for the library’s default list of systems. Use eachSystem to specify your own set of platforms.

Flake templates#

Flakes let you create templates that other people can use to initialize projects quickly with a single command.

1. View the official templates

nix flake show templates

2. Initialize a project from a template

# 初始化一个简单的 python 环境
nix flake init -t templates#simple

3. Define templates in your own Flake

You can turn your configuration into a template to share with others:

{
  outputs = { self }: {
    templates.my-rust-app = {
      path = ./templates/rust;
      description = "一个基础的 Rust 项目模板";
    };
  };
}

Why does this matter?#

On NixOS, defining your own Flake templates lets you set up development environments for different languages quickly, without having to configure PATH manually.