This is Rust we're talking about. It doesn't even need to work; as long as it compiles, it's correct.
use std::fs::File;
use std::io::prelude::*;
fn main() -> std::io::Result<()> {
let mut file = File::create("content.txt")?;
file.write_all(b"3!")?;
Ok(())
}No, it doesn't even need to compile. The mere fact that it's in Rust means it's correct.