1. In the folder src/bin, create a file called own_iterator.rs.
2. Add the following code, and run it with cargo run --bin own_iterator:

1   fn main() {
2     let fib: Vec<_> = fibonacci().take(10).collect();
3     println!("First 10 numbers of the fibonacci sequence: {:?}", 
        fib);
4 
5     let mut squared_vec = SquaredVec::new();
6     squared_vec.push(1);
7     squared_vec.push(2);
8     squared_vec.push(3);
9     squared_vec.push(4);
10    for (index, num) in squared_vec.iter().enumerate() {
11      println!("{}^2 is {}", index + 1, num);
12    }
13  }
14 
15 
16  fn fibonacci() -> Fibonacci {
17    Fibonacci { curr: 0, next: 1 }
18  }
19  struct Fibonacci {
20  curr: u32,
21  next: u32,
22  }
23  // A custom iterator has to implement
24  // only one method: What comes next
25  impl Iterator for Fibonacci {
26    type Item = u32;
27    fn next(&mut self) -> Option<u32> {
28      let old = self.curr;
29      self.curr = self.next;
30      self.next += old;
31      Some(old)
32    }
33  }
34 
35 
36  use std::ops::Mul;
37  struct SquaredVec<T>
38  where
39  T: Mul + Copy,
40  {
41    vec: Vec<T::Output>,
42  }
43  impl<T> SquaredVec<T>
44  where
45  T: Mul + Copy,
46  {
47    fn new() -> Self {
48    SquaredVec { vec: Vec::new() }
49  }
50  fn push(&mut self, item: T) {
51    self.vec.push(item * item);
52  }
53 }
54 
55  // When creating an iterator over a collection-like struct
56  // It's best to just allow it to be convertible into
57  // a slice of your underlying type.
58  // This way you automatically implemented a bunch of methods
59  // and are flexible enough to change your implementation later
      on
60  use std::ops::Deref;
61  impl<T> Deref for SquaredVec<T>
62  where
63  T: Mul + Copy,
64  {
65    type Target = [T::Output];
66    fn deref(&self) -> &Self::Target {
67    &self.vec
68  }
69 }