rustprint.rs

  struct List(Vec<i32>);
  impl fmt::Display for List {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
      // Dereference `self` and create a reference to `vec`
      // via destructuring.
      let List(ref vec) = *self;

      try!(write!(f, "["));

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

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