implement fmt::Display on a struct in Rust

impl_rust_distplay_example.rs

use std::fmt;

// IPv4 struct is just a tuple of u8's.
// just an arbitrary, but realistic example...
struct IPv4(u8, u8, u8, u8);

// declare the impl block for out IPv4 struct.
impl fmt::Display for IPv4 {
    // this is the function signature the fmt::distplay trait is looking for.
    // https://doc.rust-lang.org/std/fmt/trait.Display.html
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        // use write! macro just like println! macro, but output gets writen to
        // the formatter struct.
        write!(f, "{}.{}.{}.{}", self.0, self.1, self.2, self.3)
    }
}

fn main() {

    // notice how you simple this struct declaration is.
    // very refreshingly easy.
    let ipv4 = IPv4(192, 168, 0, 1);

    // println macro calls IPv4.fmt() on out ipv4 struct.
    // now the plrintln marco knows how to print our struct.
    println!("{}", ipv4);
}