1. Open the Cargo.toml file that was generated earlier for you.

2. If you didn't do so in the last recipe, under [dependencies], add the following line:

rayon = "1.0.0"

3. If you want, you can go to rayon's crates.io page (https://crates.io/crates/rayon) to check for the newest version and use that one instead.

4. In the folder bin, create a file called join.rs.

5. Add the following code and run it with cargo run --bin join:

1 extern crate rayon;
2 
3  #[derive(Debug)]
4  struct Rectangle {
5    height: u32,
6    width: u32,
7  }
8 
9  impl Rectangle {
10    fn area(&self) -> u32 {
11       self.height * self.width
12    }
13    fn perimeter(&self) -> u32 {
14       2 * (self.height + self.width)
15    }
16  }
17 
18  fn main() {
19    let rect = Rectangle {
20       height: 30,
21       width: 20,
22    };
23    // rayon::join makes closures run potentially in parallel and
24    // returns their returned values in a tuple
25    let (area, perimeter) = rayon::join(|| rect.area(), || 
      rect.perimeter());
26    println!("{:?}", rect);
27    println!("area: {}", area);
28    println!("perimeter: {}", perimeter);
29 
30    let fib = fibonacci(6);
31    println!("The sixth number in the fibonacci sequence is {}", 
      fib);
32  }
33 
34  fn fibonacci(n: u32) -> u32 {
35    if n == 0 || n == 1 {
36     n
37    } else {
38      // rayon::join can really shine in recursive functions
39      let (a, b) = rayon::join(|| fibonacci(n - 1), || fibonacci(n 
          - 2));
40       a + b
41    }
42  }