Collections, ownership, and borrowing

Store values in collections and choose when to transfer, copy, or borrow them.

1. Build and update a list
2. Transfer or copy ownership
3. Take part of a list or text
4. Borrow a collection
5. Borrow an element
6. Handle allocation failures
7. Associate keys with values Optional lookup handles missing entries explicitly.
8. Keep distinct values in a set
9. Remove values and take ownership
10. Group different types in tuples
11. Sort and reorder a list
12. Clean up owned values
13. Build singly and doubly linked lists

The collection examples provide additional operations.