Refactoring 2 TheMaxRefactoring 2 TheMax

Diego Guidi & Alfredo MorresiDiego Guidi & Alfredo Morresistaff@dotnetmarche.orgstaff@dotnetmarche.org

Shit happensShit happens

Anything that can go wrong will go Anything that can go wrong will go wrong.wrong.

(Arthur Bloch)(Arthur Bloch)

UnderengineeringUnderengineering

AKA "fast, slow, slower.... never :("AKA "fast, slow, slower.... never :(" quickly deliver 1.0 release that works well for our quickly deliver 1.0 release that works well for our

customers but with junky codecustomers but with junky code working on 2.0 release, junky code slows you down, working on 2.0 release, junky code slows you down,

and new features are harder to implementand new features are harder to implement as junky code multiplies, people lose faith into the as junky code multiplies, people lose faith into the

system and the programmerssystem and the programmers planning next release, you realize you can't win, and planning next release, you realize you can't win, and

start thinking about a total rewritestart thinking about a total rewrite

OverengineeringOverengineering

AKA "the 'HelloWorld' pattern"AKA "the 'HelloWorld' pattern" code more sophisticated that it possible future code more sophisticated that it possible future

requirementsrequirements code hard to understand for new onescode hard to understand for new ones time wasted understanding and maintaining complex time wasted understanding and maintaining complex

code so you need to write documentationcode so you need to write documentation

Code smellsCode smells

copy/paste (duplicate) codecopy/paste (duplicate) code large method/classlarge method/class method-like propertiesmethod-like properties contrived complexity (patterns everywhere!)contrived complexity (patterns everywhere!) inappropriate intimacyinappropriate intimacy unused codeunused code dangerous if (if - else if - else if - else...)dangerous if (if - else if - else if - else...)

Cunningham's metaphorCunningham's metaphor

The technical language doesn't communicate The technical language doesn't communicate effectively with the vast majority of management. effectively with the vast majority of management. Instead, Ward Cunningham's financial metaphor of Instead, Ward Cunningham's financial metaphor of design debt works infinitely better.design debt works infinitely better.Design debt occurs when you don't consistently do Design debt occurs when you don't consistently do three things.three things.1. Remove duplication.1. Remove duplication.2. Simplify your code.2. Simplify your code.3. Clarify you code's intent.3. Clarify you code's intent.

Cunningham's metaphorCunningham's metaphor

Few systems remain completely free of design debt. Few systems remain completely free of design debt. Wired as we are, humans just don't write perfect code Wired as we are, humans just don't write perfect code the first time around. We naturally accumulate design the first time around. We naturally accumulate design

debt. So the question becomes:debt. So the question becomes:

"When do you pay it down?""When do you pay it down?"

And so, refactoring!And so, refactoring!

Refactoring is the process of changing a software Refactoring is the process of changing a software system in such a way that it does not alter the external system in such a way that it does not alter the external

behavior of the code yet improves its internal behavior of the code yet improves its internal structure.structure.

A refactoring is a "behavior-preserving transformation" A refactoring is a "behavior-preserving transformation" or, as Martin Fowler defines it, "a change made to the or, as Martin Fowler defines it, "a change made to the

internal structure of software to make it easier to internal structure of software to make it easier to understand and cheaper to modify without changing its understand and cheaper to modify without changing its

observable behavior"observable behavior"

Why refactoring?Why refactoring?

Code i wrote yesterday is worse that code i'm writing Code i wrote yesterday is worse that code i'm writing todaytoday

Make it easier to add new codeMake it easier to add new code Improve the design of existing codeImprove the design of existing code Gain a better understanding of codeGain a better understanding of code Make coding less annoyingMake coding less annoying Readability / Testability / EstensibilityReadability / Testability / Estensibility bugs correctionbugs correction ......

When refactoring?When refactoring?

Keeping code clean is a lot like keeping a room Keeping code clean is a lot like keeping a room clean. Once your room becomes a mess, it becomes clean. Once your room becomes a mess, it becomes harder to clean. The worse the mess becomes, the harder to clean. The worse the mess becomes, the less you want to clean it.less you want to clean it.

It's best to refactor continuously, rather than in It's best to refactor continuously, rather than in phases. When you see code that needs phases. When you see code that needs improvement, improve it.improvement, improve it.

On the other hand, if your manager needs you to On the other hand, if your manager needs you to finish a feature before a demo that just got finish a feature before a demo that just got scheduled for tomorrow, finish the feature and scheduled for tomorrow, finish the feature and refactor later!refactor later!

When NOT refactoring?When NOT refactoring?

If it's working, don't changeIf it's working, don't change if you have a poorly factored programif you have a poorly factored program if your code isn't tested, that does what the if your code isn't tested, that does what the

customer wants and has no serious bugs, leave it customer wants and has no serious bugs, leave it alone!alone!

performance matters...performance matters...

How refactoringHow refactoring

Refactoring recipesRefactoring recipes extract superclass/interfaceextract superclass/interface rename method/property/variablerename method/property/variable replace conditional with polymorphismreplace conditional with polymorphism replace constructor with factory methodreplace constructor with factory method inline methodinline method even more: even more: http://www.refactoring.com/cataloghttp://www.refactoring.com/catalog

How refactoringHow refactoring

Only refactor when refactoring -- do not add feature Only refactor when refactoring -- do not add feature during refactoring.during refactoring.

Refactoring, or improving the design of existing code, Refactoring, or improving the design of existing code, requires that you know what code needs improvement. requires that you know what code needs improvement.

How refactoringHow refactoring

Each transformation (called a "Refactoring") does little, Each transformation (called a "Refactoring") does little, but a sequence of transformations can produce a but a sequence of transformations can produce a

significant restructuring.significant restructuring.

The system is also kept fully working after each small The system is also kept fully working after each small refactoring, reducing the chances that a system can refactoring, reducing the chances that a system can

get seriously broken during the restructuring process.get seriously broken during the restructuring process.

How refactoringHow refactoring

If you want to refactor, the essential If you want to refactor, the essential precondition is having solid testprecondition is having solid test

(Martin Fowler)(Martin Fowler)

Test-Driven DevelopmentTest-Driven Development

Test-driven development (TDD) and continuous Test-driven development (TDD) and continuous refactoring enable the efficient evolution of working refactoring enable the efficient evolution of working

code by turning programming into a dialogue.code by turning programming into a dialogue.

Test-Driven DevelopmentTest-Driven Development

AskAsk: You ask a question of a system by writing a test.: You ask a question of a system by writing a test.RespondRespond: You respond to the question by writing : You respond to the question by writing code to pass the test.code to pass the test.RefineRefine: You refine your response by consolidating : You refine your response by consolidating ideas, weeding out inessentials, and clarifying ideas, weeding out inessentials, and clarifying ambiguities.ambiguities.RepeatRepeat: You keep the dialogue going by asking the : You keep the dialogue going by asking the next question.next question.

Refactoring and patternRefactoring and pattern

There is a natural relation between There is a natural relation between patterns and refactorings. Patterns patterns and refactorings. Patterns

are where you want to be; are where you want to be; refactorings are ways to get there refactorings are ways to get there

from somewhere else.from somewhere else.(Fowler Martin)(Fowler Martin)

Refactoring and patternRefactoring and pattern

Each pattern is a three-part rule, which expresses a Each pattern is a three-part rule, which expresses a relation between a certain context, a problem, and a relation between a certain context, a problem, and a solution.solution.

There are many ways to implement a pattern. If you There are many ways to implement a pattern. If you don't know patterns, you're less likely to evolve great don't know patterns, you're less likely to evolve great designs. Patterns capture wisdom. Reusing that designs. Patterns capture wisdom. Reusing that wisdom is extremely useful, also when refactoring.wisdom is extremely useful, also when refactoring.

ReadingsReadings

Refactoring: Improving the Design of Existing Code Refactoring: Improving the Design of Existing Code (Martin Fowler)(Martin Fowler)

Refactoring to patternsRefactoring to patterns(Joshua Kerievsky)(Joshua Kerievsky)

Design Patterns: Elements of Reusable Object-Design Patterns: Elements of Reusable Object-Oriented SoftwareOriented Software(Gang of Four)(Gang of Four)

The Pragmatic ProgrammerThe Pragmatic Programmer(Andrew Hunt and David Thomas)(Andrew Hunt and David Thomas)

The sage final sentenceThe sage final sentence

Any fool can write code Any fool can write code that a computer can that a computer can

understand. Good understand. Good programmers write code programmers write code

that humans can that humans can understand.understand.

(M. F.)(M. F.)

Questions?Questions?

The Must-Have Productivity Tool for .NET DevelopersThe Must-Have Productivity Tool for .NET Developers

PROsPROs intellisenseintellisense code searchcode search test runnertest runner code generationcode generation background analysisbackground analysis

CONsCONs commercial licensecommercial license needs a lot of ram!needs a lot of ram! a little bit buggya little bit buggy