error[E0412]: cannot find type `HashMap` in this scope
 --> src/main.rs:2:8
  |
2 |     m: HashMap<String, ()>,
  |        ^^^^^^^ not found in this scope
  |
help: consider importing one of these items
  |
1 | use std::collections::HashMap;
  |
1 | use std::collections::hash_map::HashMap;
  |