Chapter 2: Designing Classes with a Single Responsibility

Question 1

What is considered as a TRUE code?

Answer 1

A code that is:

• Transparent
• Reasonable
• Usable
• Exemplary

Question 2

What does a TRUE code measure?

Answer 2

That a code written now will be easily changed in the future

Question 3

What does a Transparent code mean?

Answer 3

The consequences of change should be obvious in the code that is changing now and in distant code that relies on it

Question 4

What does a Reasonable code mean?

Answer 4

The cost of any change should be proportional to the benefits the change archives

Question 5

What does a Usable code mean?

Answer 5

Existing code should be usable in new and unexpected contexts

Question 6

What does an Exemplary code mean?

Answer 6

The code itself should encourage those who change it to perpetuate the qualities it has

Question 7

What is the first step in creating code that is TRUE?

Answer 7

It is to ensure that each class has a single, well-defined responsibility

Question 8

How do you determine if a class has Single Responsibility?

Answer 8

• You can ask questions using the method names
• You can create sentences with the methods names and check if you need conjunctions like ‘and’ or ‘or’ to build the sentence, if so, maybe the method are doing too much.

Question 9

What is Cohesion?

Answer 9

When everything in a class is related to its central purpose.

Question 10

What are the techniques to create code that embraces changes?

Answer 10

Depend on behavior, not data
- Hide instance variables
- Hide data structures
Enforce Single Responsibility everywhere
- Extract extra responsibilities from methods
- Isolate Extra Responsabilities in classes

Question 11

How does the “Hide instance variables” technique work?

Answer 11

Always wrap instance variables in accessor methods instead of directly referring to them.

Question 12

How does the “Hide data structures” technique work?

Answer 12

You need to separate structure from meaning. For this, we can use the Ruby Struct class to wrap a strucuture

Question 13

What are the benefits of use methods that have single responsability?

Answer 13

• Expose previously hidden qualities
• Avoid the need for comments
• Encourage reuse
• Are easy to move to another class