Extracting Data Clumps

In legacy code we often lack abstractions. How do we find these missing abstractions? Following code smells gives some ideas.

Learning Goals

Recognize code smells Data Clump and Long Parameter List.
Perform extract C-style struct, record or (data) class in a safe way.
Find a name for the new abstraction.

Session Outline

5 min Connect: Sort concepts according its relation to abstraction
20 min Concept: Explain code smells and how to refactor them
30 min Concrete practice: Identify Data Clumps, extract them, name them
5 min Conclusion: Discuss Open Question

Sort the following concepts according its relation to abstraction (i.e. grouping of related data and logic). There are four in each row, sort by highest relevancy.

grouping is related to abstraction
- Modularity (reason: structure a system)
- Encapsulation (reason: information hiding)
- Reusability (reason: because in one piece)
- Maintainability (reason: easier to locate and understand)
not related
- Scalability
- Performance
- Concurrency
- Usability

Concept - Data Clump and Long Parameter List

Lecture using slides or frames about how we could find these missing abstractions? One way is to follow up on some code smells. Explain the code smells and show sample code.

Data Clump

Different parts of the code contain identical groups of variables.
These clumps should be turned into their own classes.

Long Parameter List

More than three or four parameters for a method.

Scan code for these code smells

Code Review: As first exercise, check out the code and look for Data Clumps and Long Parameter Lists. Allow people 5 minutes looking at the code. Then collect the group and ask what they found.

Demo

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

There is a data clump of a Student declared and used in a method.
Define a struct to represent a Student.
Create an instance of the Student struct with same values.
Add the Student struct to the method signature and pass the instance (parallel change).
Use the Student struct in the method’s body (parallel change).
Remove the data clamp from the method signature, now use the struct to pass Student information alone.
Remove the declared data clump of the Student data.

Concrete Practice - Hero Quest

The Hero Quest Refactoring Kata contains some pieces of code from a RPG dealing with players and items. People work in pairs and follow the code smells to extract data clumps.

Facilitation Hints

In half an hour people can do one to two iterations, i.e. converting one to two data clumps and using them in one method each.

Conclusions - Summarise Usage

Ask the group what indications for missing abstraction could there be? How do you recognise these, when you need to introduce an abstraction?

Expected answers are

Data Clump code smell
Long Parameter List code smell