Clean Code - 6 Objects and Data Structures

Data Abstraction

Hiding implementation is about abstractions!

To not expose the details of data, use:

• interface
• getters and setters

Data/Object Anti-Symmetry

Objects hide their data behind abstractions and expose functions that operate on that data.

Objects and data structures are different

• Objects
  • Data is hidden behind abstractions, and use getters and setters (expose functions) to operate data
• Data structure
  • Data is exposed to the outside, and there are no meaningful functions

OOP solution

Polymorphism

Procedural code (code using data structures) vs OO code

	Procedural code	OO code
Easy when..	Add new functions (no need to change the existing data structure)	Add new classes (no need to change the existing functions)
Hard when..	Add new data structure (need to change all existing functions)	Add new functions (need to change all existing classes )
When to use	Want to add new functions instead of new types	Want to add new types than new functions

the idea that everything is an object is a myth. Sometimes you do want simple data structures with procedures operating on them.

The Law of Demeter

a module should not know about the innards of the objects it manipulates.

Another good resource to read:
https://betterprogramming.pub/demeters-law-don-t-talk-to-strangers-87bb4af11694

Train Wrecks

Chains of calls like this are generally considered to be sloppy style and should be avoided.

When ctxt, Options, and ScratchDir are merely data structures without behaviors, the following codes do not violate the Law of Demeter:

const outputDir: string = ctxt.options.scratchDir.absolutePath;

Hybrids

half object and half data structure.

hybrids make it hard to add new functions but also make it hard to add new data structures. So should avoid using it.

Hiding Structure

When ctxt, options, and scratchDir are objects with real behavior:

• We should ask it to do something instead of knowing how it works inside

Data Transfer Objects

Quintessential form of a data structure (data transfer object, or DTO):

• A class that has public variables but does not have functions
• Useful for databases communication, or parsing messages from sockets

Active Record

• Special forms of Data Transfer Objects
• Are data structures with public variables
• Usually have navigational methods such as save and find
• The good practice is to treat Active Record as data structures

Conclusion

Objects expose behavior and hide data; Data structures expose data and have no significant behavior.

More flexible when:

	Objects	Data types and procedures
Add new data types	V
Add new behaviors		V

tags: learn clean code test automation