A First Set of Refactorings

本篇同步发文於个人网站: A First Set of Refactorings

This article references the chapter 6 ” A First Set of Refactorings ” of Refactoring: Improving the Design of Existing Code (2nd Edition). Author had highlighted many important refactorings in this chapter.

I use .NET C# to practice with these refactorings and upload to Github.

(Photo from Pixabay: https://pixabay.com/illustrations/plumber-repair-tools-pipe-plunger-4427401/ )

Extract Function

Tips

• Redundant logics should be extracted as a function
• A function is best when developers see its naming and understand what it does without looking at its implementation.
• A function usually has few lines of code.
• Sometimes a extracted function is not proper, then transfer it into inline lines.

Examples:

• No Variables Out of Scope
• Using Local Variables
• Reassigning a Local Variable

Github

Inline Function

Tips

• If the indirect call of this function is not required, make it as inline function
• This function has no polymorphism. It means that if this function belongs to a class and subclass uses it, inline function doesn’t work.

Examples:

• Rating
• Report Lines

Github

Extract Variable

Tips

• Some expressions are complex, so use Extract Variable to improve readability.
• Check the target expression has no side-effect before extract it

Examples:

• Static Function
• In a Class

Github

Inline Variable

Tips

• If this variable hinders the nearby refactoring, this variable should be removed.
• Check the right side of the assignment to the variable has no side-effect.

Examples:

int grade = student.Grade;
return (grade >= 60);

// after Inline Variable

return student.Grade >= 60;

Change Function Declaration

Tips

• A good function name increases readability.
• Changing parameters of a function decouple between the modules.
• If an published API should be refactored, then use [deprecated] for the original function. After a period, migrate the old function to the new one and remove the old one.

Examples:

• Renaming a Function (Simple Mechanics)
• Renaming a Function (Migration Mechanics)
• Adding a Paramete
• Changing a Parameter to One of Its Properties

Github

Encapsulate Variable

Tips

• Usually use function to encapsulate access of variables
• For mutable data, if its scope exceeds one function, we encapsulate it.
• If the variable’s value is a record, we can use Encapsulate Record

Examples:

• Simple
• Encapsulating the Value

Github

Rename Variable

Tips

• Good naming increases readability
• If the variable is widely used, we can use Encapsulate Variable
• If this variable is a published variable, we can’t use this refactoring

Examples:

• Encapsulating Variable
• Renaming a Constant

Github

Introduce Parameter Object

Tips

• Use a class to packs the parameters of a function
• Keep these classes as Value Objects (DDD)
• Use Change Function Declaration to create the new class parameter

Examples:

• Change Function Declaration

Github

Combine Functions into Class

Tips

• If some parameter exists in multiple functions, creating a class is a good choice. Move the parameter to class field and reduce parameter of function.
• Combine Functions into Transform is another choice depending on the context
• Use Encapsulate Record for the previously mentioned parameters. Then use Move Function for those function into a new class.
• We can use Extract Function for the logic processing the record data into the new class.

Examples:

Github

Combine Functions into Transform

Tips

• Transform function loads the original data, then use some functions to get new data and set it the fields of derivation data.
• Comparing with Combine Functions into Class, if some code logic updates the original data, Combine Functions into Class is better.
• In a transform function, first deep copy the loaded original data into result(derivation) data. Finally return this result data.
• If the structure of the result is the same as the original, the transform function uses “Enrich” as prefix naming. If the structure changes, then use “Transform” as prefix naming.
• It’s not recommended for JavaScript to use this refactoring instead of using Combine Functions into Class because of Immutable data

Examples:

Github

Split Phase

Tips

• If some logic concurrently processes 2 different things, then separate it into 2 independent modules.
• Extract the second phase code as a new function. And create an intermediate data structure as the parameter of the new function.
• If some parameters in second phase are used by first phase, then move these parameters into the intermediate data structure.
• Extract the first phase as a function and this function returns the intermediate data structure.

Examples:

Github

Conclusion

This chapter introduces me to a whole clever coding environment! I think I ever did some similar refactorings in my previous projects without so detailed guidelines. If you want to learn detailed motivation and mechanics, study the chapter 6 ” A First Set of Refactorings ” of Refactoring: Improving the Design of Existing Code (2nd Edition). and it improves our programmer’s ability.