How to do it...

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

1   use std::collections::HashSet;
2 
3   fn main() {
4     // Most of the interface of HashSet
5     // is the same as HashMap, just without
6     // the methods that handle values
7     let mut books = HashSet::new();
8     books.insert("Harry Potter and the Philosopher's Stone");
9     books.insert("The Name of the Wind");
10    books.insert("A Game of Thrones");
11 
12    // A HashSet will ignore duplicate entries
13    // but will return if an entry is new or not
14    let is_new = books.insert("The Lies of Locke Lamora");
15    if is_new {
16      println!("We've just added a new book!");
17    }
18 
19    let is_new = books.insert("A Game of Thrones");
20    if !is_new {
21      println!("Sorry, we already had that book in store");
22    }
23 
24    // Check if it contains a key
25    if...