Elixir is great for many things, but sometimes you need raw speed or access to native libraries. That’s where Native Implemented Functions (NIFs) come in. This post walks through creating a simple Elixir NIF using Rust with the help of the rustler crate.

Set up your Elixir project

Start with a basic Elixir application:

mix new my_nif_app
cd my_nif_app

Add :rustler as a dependency in mix.exs:

defp deps do
  [
    {:rustler, "~> 0.38.0"}
  ]
end

Fetch the dependencies:

mix deps.get

Generate the Rust NIF scaffold

$ mix rustler.new
This is the name of the Elixir module the NIF module will be registered to.
Module name > MyNif
This is the name used for the generated Rust crate. The default is most likely fine.
Library name (mynif) > my_nif
Fetched latest rustler crate version: 0.39.0
* creating native/my_nif/README.md
* creating native/my_nif/Cargo.toml
* creating native/my_nif/src/lib.rs
* creating Cargo.toml
Updating .gitignore file

Ready to go! See native/my_nif/README.md for further instructions.

This command will:

• Create a native/ directory
• Scaffold a Rust crate
• Link it into your Elixir project

Choose a crate name when prompted, such as my_nif.

Write a simple NIF in Rust

Open the generated native/my_nif/src/lib.rs file and replace its contents with:

#[rustler::nif]
fn add(a: i64, b: i64) -> i64 {
    a + b
}

rustler::init!("Elixir.MyNif");

This defines a basic add/2 function exposed to Elixir.

Define the Elixir wrapper

In lib/my_nif.ex, wire up the NIF:

defmodule MyNif do
  use Rustler, otp_app: :my_nif_app, crate: "my_nif"

  # Fallback when the NIF is not loaded
  def add(_a, _b), do: :erlang.nif_error(:nif_not_loaded)
end

Build and test

Compile the NIF:

mix compile

Then try it out in iex:

$ iex -S mix
iex> MyNif.add(2, 3)
5

You've created a simple Elixir NIF using Rust. This lets you use Rust's performance and ecosystem while retaining Elixir's productivity.