DRY is our mantra. Teachers tell us to remove duplication. We need to go beyond.
Problems
Code Duplication
Maintainability
Solutions
Find repeated patterns (not repeated code).
Create an abstraction.
Parametrize abstraction calls.
Use composition and never inheritance.
Unit test new abstraction.
Sample Code
Wrong
<? | |
class WordProcessor { | |
function replaceText(string $patternToFind, string $textToReplace) { | |
$this->text = '<<<' . | |
str_replace($patternToFind, $textToReplace, $this->text) | |
. '>>>'; | |
} | |
} | |
final class Obfuscator { | |
function obfuscate(string $patternToFind, string $textToReplace) { | |
$this->text = | |
strlower(str_ireplace( | |
$patternToFind, $textToReplace, $this->text)); | |
} | |
} |
Right
<? | |
final class TextReplacer { | |
function replace( | |
string $patternToFind, | |
string $textToReplace, | |
string $subject, | |
string $replaceFunctionName, | |
$postProcessClosure) { | |
return $postProcessClosure( | |
$replaceFunctionName($patternToFind, | |
$textToReplace, | |
$subject)); | |
} | |
} | |
// Lots of tests on text replacer so you can gain confidence. | |
final class WordProcessor { | |
function replaceText(string $patternToFind, string $textToReplace) { | |
$this->text = (new TextReplacer())->replace( | |
$patternToFind, | |
$textToReplace, | |
$this->text, | |
'str_replace', fn($text) => '<<<' . $text . '>>>'); | |
} | |
} | |
final class Obfuscator { | |
function obfuscate(string $patternToFind, string $textToReplace) { | |
$this->text = (new TextReplacer())->replace( | |
$patternToFind, | |
$textToReplace, | |
$this->text, | |
'str_ireplace', fn($text) => strlower($text)); | |
} | |
} |
Detection
Linters can find repeated code.
There are not very good finding similar patterns.
Maybe soon machine learning will help us find such abstractions automatically.
For now, it is up to us, humans.
Tags
- Duplication
Conclusion
Repeated code is always a smell.
Copying and pasting code is always a shame.
With our refactoring tools, we need to accept the duplication remove challenge trusting our tests as a safety net.
Relations
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Code Smell 11 - Subclassification for Code Reuse
Maxi Contieri ・ Oct 30 '20
More info
Credits
Photo by Sid Balachandran on Unsplash
Copy and paste is a design error.
David Parnas
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