Programming custom apps on the 3DS platform can be hard, since it's mostly being written in C/C++. However, we can write apps with Rust, thanks to the amazing tools provided by the Rust community.

Dependencies

You must install devkitPro, to get the 3DS's toolchain. Follow the instructions here

Setting up a project

First, we'll initialize the project as usual, by running cargo new rust_3ds. Enter the new directory, and run cargo add --git https://github.com/Rust3DS/ctru-rs ctru-rs. This will add a partial std implementation among other things. We must also install cargo-3ds, a tool to help build our project for the 3DS. Just run cargo install --git https://github.com/Rust3DS/cargo-3ds.

Now that we have our project, we will have to make our first modification. Open up src/main.rs and replace the code with:

use ctru::prelude::*;

fn main() {
    ctru::use_panic_handler();
    
    //Initialize the controllers
    let gfx = Gfx::new().unwrap();
    let mut hid = Hid::new().unwrap();
    let apt = Apt::new().unwrap()
    
    //Optional => Initializes networking
    let soc = Soc::new().unwrap();

    let _console = Console::new(gfx.top_screen.borrow_mut());

    while apt.main_loop() {
        hid.scan_input();

        if hid.keys_down().contains(KeyPad::A) {
            break;
        }

        gfx.wait_for_vblank();
    }
}

To build it, run cargo 3ds build. You can move the new .3dsx file on to your 3DS and run it via the Homebrew Launcher.

From my experience, I have had errors building bigger projects. To solve this, you must add the following to your Cargo.toml

[profile.dev]
opt-level = 1

[profile.release]
opt-level = 3
lto = true
overflow-checks = false