//Import the `fmt` module.
use std::fmt;

//Define a structure named `List` containing a `Vec`.
struct List(Vec<i32>);

impl fmt::Display for List{
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result{
		//Extract the value using tuple indexing,
		//and create a reference to `vec`.
		let vec = &self.0;

		write!(f, "[")?;

		//Iterate over `v` in `vec` while enumerating the iteration count in `count`.
		for(count, v) in vec.iter().enumerate(){
			//For every element except the first, add a comma.
			//Use the ? operator, or try!, to return on errors.
			if count != 0{
				write!(f, ", ")?;
			}
			write!(f, "{}: {}", count, v)?;
		}

		//Close the opened bracket and return a fmt::Result value.
		write!(f, "]")
	}
}

fn main(){
	let v = List(vec![1, 2, 3]);
	println!("{}", v);
}