Hello World!

Here’s one of the simplest vexide programs that can be written, printing a short message to the terminal:

#![no_std]#![no_main]use vexide::prelude::*;#[vexide::main]async fn main(peripherals: Peripherals) {    println!("Hello World!");}

Let’s go through this one part at a time.

#![no_std] and #![no_main]

These two declarations at the top of our file tell the rust compiler two things:

• We don’t want the Rust standard library (the std crate), since it requires an operating system.
• We don’t want a regular Rust main function, since that requires a C runtime, which we also do not have.

Both of these declarations are necessary for programs to run on the V5’s embedded hardware. Rather than std we will be using the core crate (which provides most functionality of std), and vexide implements its own entrypoint and startup process that doesn’t require a C runtime.

The vexide Prelude

#![no_std]#![no_main]use vexide::prelude::*;#[vexide::main]async fn main(peripherals: Peripherals) {    println!("Hello World!");}

This piece of code brings vexide’s prelude module into scope. All that this does is import a bunch of commonly used types for you, so you don’t have to type their full name every time. For example, you can simply use Motor rather than vexide::devices::smart::motor::Motor.

The Program Entrypoint

All vexide programs begin and end at the main function, which must have the #[vexide::main] attribute on it.

#![no_std]#![no_main]use vexide::prelude::*;#[vexide::main]async fn main(peripherals: Peripherals) {    println!("Hello World!");}

If you’re familiar with Rust, you might notice some key differences in vexide’s version of the main function compared to a normal main function in Rust:

1. main is an async fn. vexide ships with its own async runtime that serves as the basis for its multitasking features. In order to run other async functions, main itself must also be async.
2. main takes a peripherals argument. This is an instance of the Peripherals struct that allows you to create devices and interact with hardware. You can read more about that here.
3. main is annotated with #[vexide::main]. This is a special attribute macro that sets up the real program entrypoint. Behind the scenes, it performs some lowlevel startup and sets up vexide’s async executor running your code.