```
fn main() {
println!("Hello, world!");
}
```
Discussion
```
fn main() {
let name = "world!";
println!("Hello, {}", name);
}
```
```
struct Greeting {
name: String,
}
fn main() {
let greeting = Greeting{ name: "world!".to_string()};
println!("Hello, {}", greeting.name);
}
```
```
struct Greeting {
name: String,
}
impl Greeting {
fn new(name: &str) -> Self {
Greeting {
name: name.to_string(),
}
}
}
fn main() {
let greeting = Greeting::new("world!");
println!("Hello, {}", greeting.name);
}
```