Hello World in Rust

Welcome to the Hello World in Rust page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

fn main() {
    println!("Hello, World!");
}

Hello World in Rust was written by:

• Jeremy Griffith

This article was written by:

• Jeremy Grifski
• Johnny Fang
• rzuckerm
• shubhragupta-code

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

In fact, Rust's implementation is even easier. There's no need to import any IO packages to get access to println. We just need to create our main function, add our print code, and we're done.

But, wait a minute. That print line seems a little off. What's with the bang !? To be honest, I had to do a bit of digging for this. As it turns out, println is not a function at all. It's a built-in macro. That's a new term for me, so let's learn a little more about it.

According to the Rust Programming Language book, macros are a language feature that allow you to abstract syntax. In other words, macros allow you to do some metaprogramming by adding grammar to Rust's abstract syntax tree. Perhaps an example would make more sense:

macro_rules! println {
    () => {
        $crate::print!("\n")
    };
    ($($arg:tt)*) => {{
        $crate::io::_print($crate::format_args_nl!($($arg)*));
    }};
}

This is the actual definition of the println macro in Rust (click on "source"). I won't go into exactly what's happening, but basically we have defined two available patterns for println: empty and variable arguments. Rust functions don't have support for variable arguments, so you can add the functionality with macros.

That said, I'm only just learning macros for the first time, so I recommend an article by Kasper Andersen called why Rust has macros. It's quite thorough, and I think it does a better job than Rust's documentation.

How to Run the Solution

As always, we can try out this code using an online Rust compiler. All we need to do is drop the code into the editor and hit run.

Alternatively, we can download the latest Rust compiler and a copy of the solution. Then, assuming the compiler is in the path, navigate to folder with the solution and run the following in Windows:

rustc hello-world.rs
hello-world.exe

Of course, in Unix-based environments, the following will run the new binary:

./hello-world

And, that's it! "Hello, World!" should print directly to the console.