Added program to teach how to write display

functions for itteratable structures

testcase.rs

@@ -0,0 +1,33 @@
+//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);
+}