Code Smell 46 - Repeated Code
28 January, 2023
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Contributors
Problems
- Code Duplication
- Maintainability
- Don't Repeat Yourself
Solutions
- Find repeated patterns (not repeated code).
- Create an abstraction.
- Parametrize abstraction calls.
- Use composition and never inheritance.
- Unit test new abstraction.
Examples
Sample Code
Wrong
<?
final 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 we 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 removal challenge trusting our tests as a safety net.
Relations
Code Smell 11 - Subclassification for Code Reuse
More Info
%[https://en.wikipedia.org/wiki/Copy_and_paste_programming]
https://deepdive.hashnode.dev/dry-dont-repeat-yourself
Credits
Photo by Sid Balachandran on Unsplash
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Copy and paste is a design error.
David Parnas
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Software Engineering Great Quotes
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This article is part of the CodeSmell Series.