Data structures

Learning objectives

• Practice to use classes for expression
• Practice to use classes for type safety
• Understand difference between composition and aggregation
• Practice to use composition for a 'has-a' relationship

Data structures

Good data structures:

• Increase expressiveness
• Bundles data that belongs together
• Ensures correct state of the program

Good example data structures are built-in data structures.

Discussion

• Structures increase expressiveness of code
• The design of data structures has implications
• Structures are useful to bundle data
• It is rare that structures match the real world

structure versus class

Parameter	structure	class
Python keyword	class	class
R object type	S3 class	S4, R5, R6
All states are valid	Yes	No
Maintains a valid state	No	Yes
Example	A number for an x coordinate	A string for a DNA sequence
Invalid when	Never	Sequence holds an invalid nucleotide letter