Using a HashSet

The best way to describe a HashSet is by describing how it's implemented: HashMap<K, ()>. It's just a HashMap without any values!

The two best reasons to choose a HashSet are:

• You don't want to deal with duplicate values at all, as it doesn't even include them.
• You plan on doing a lot (and I mean a lot) of item lookup - that is the question, Does my collection contain this particular item?. In a vector, this is done in
  
  , while a HashSet can do it in
  
  .

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...