From Struct to Class

After extracting Data Clumps to (C style) structs, we want to go further and make real classes.

Learning Goals

• Know the benefits of grouping into classes.
• Perform conversion of C-style struct, record or (data) class to real (C++ style) class in a safe way.
• Encapsulate the data of the new abstraction.

Session Outline

• 5 min Connect: Web Hunt on Information Hiding
• 10 min Concept: Demo Converting Struct to Class
• 35 min Concrete practice: Hero Quest (with structs)
• 5 min Conclusion: Summarise Benefits

Connect - Web Hunt on Information Hiding

Web Hunt on the following question: What is Information Hiding? What is Encapsulation? Why do we want them?

• Let participants search the web and collect key concepts.
• For example, start with Wikipedia, https://en.wikipedia.org/wiki/Information_hiding

The following things could come up:

• hides complexity
• eases re-usability
• increases readability
• helps with testing
• protect internal stuff
• etc.

Besides the connect part, this helps you to assess if participants know the theory.

Concept - Converting Struct to Class

Start with Lecture of two slides to summarise both concepts:

Information Hiding:

• Means restricting direct access to some of the module’s components.
• Usually hides implementation details like data structure or algorithm used.

Encapsulation:

• Is (usually) an object oriented term.
• Objects are defined by what they do, not what they contain.
• All data should be hidden within its class.

Demo

Do a 5 minute demo how to convert a struct to a class (recording or slides). Using an example of a student struct the following steps are necessary:

• There is a struct of a Student declared and used in some methods.
• Convert the struct to a class. And remove “struct” in all signatures.
• Create a public constructor for initialisation.
• Use the constructor for initialisation.
• Copy methods working on the class into the class (parallel change).
• Replace the main parameter with the this pointer.
• Call the instance method instead of stand alone one (parallel change).
• Remove stand alone method(s).
• Make fields private to encapsulate them.
• Rename methods accordingly the new context.

Concrete Practice - Hero Quest

The Hero Quest Refactoring Kata contains some pieces of code from a RPG dealing with players and items. Either continue after the previous learning hour or use the branch with_struct, where the structs have been created. People work in pairs and follow the steps to convert the existing structs to classes in a safe way. They also need to encapsulate their data.

Facilitation Hints

In half an hour people can do one iteration, i.e. convert one class and moving one or two methods into it.

Conclusions - Summarise Benefits

Ask the group to summarise the benefits of grouping data and methods together. Also ask for encapsulation.