struct

1. Create simple struct
2. Change attributes of a mutable struct
3. Implement a method for a struct
4. Struct method to modify fields
5. Struct inheritance
6. Struct composition: Circle
7. Struct composition: Line
8. Struct with vector of structs - Polygon
9. Printing struct fails
10. Print struct - implement Display
11. Debug struct - implement Debug
12. Derive Debug for struct
13. Struct with vector and optional value
14. Printing and debug-printing simple struct
15. Use a tuple as a struct to represent color
16. Add method to tuple-based struct
17. Struct with method
18. Structs and circural references
19. new method with default values for struct
20. The new method has no special feature
21. Default values
22. Default for composite struct
23. Compare structs for Equality
24. Compare structs for Equality - manual implementation
25. Compare structs for partial equality - PartialEq
26. Compare structs for ordering (sorting) - Ord
27. Compare structs for partial ordering (sorting) - PartialOrd
28. Manually implement ordering
29. Copy attributes from struct instance
30. Drop - destructor
31. Exercise - struct for contact info
32. Solution - struct for contact info