Introduction to Clean Code

Clean code
Cleaner, cleaner, cleaner!

What is clean code?
Clean code

Clean code
Code example: product XML-feed parser
class FeedParser
{
public function doParse()
{
$products = array(); //array of products to return
$xml = simplexml_load_file("/tmp/products.xml"); //read xml file
if ($xml === FALSE) {
throw new Exception("feed not found"); //file not found
} else {
if (count($xml) === 0) {
throw new Exception("empty feed");
} else {
foreach($xml as $elem) {
$prod = $this->parse_elem($elem);
array_push($products, $prod); //add Product object
}
}
}
return $products;
}
(...)

Clean code
http://bit.ly/seminariUPCexample
class FeedParser
{
(...)
private function parse_elem($elem)
{
$name = $this->getElementErrorHandler($elem, "title");
$url = $this->getElementErrorHandler($elem, "link");
//Product not active
return new Product($name, $url, $elem->id, false);
}
private function getElementErrorHandler($elem, $attr) {
$item = (string)$elem->$attr;
if ($item == "") {
throw new Exception("incorrect item");
}
return $item;
}
}

● Code surface
○ Code style, DRY (duplication), comments
● Naming
● Easier functions
● Cleaner logic
○ Guards, configuration over hardcoding
Clean code
Index

Clean code
Code style: let’s find fails
class FeedParser
{
(...)
{
}
private function getElementErrorHandler($elem, $attr) {
$item = (string)$elem->$attr;
if ($item == "") {
throw new Exception("incorrect item");
}
return $item;
}
}

● A repository with n developers should look homogeneous
● Code style (CS) tools
○ Verification
○ Automatic fixer
Clean code
Code style

● Impatient duplication
○ copy it and make a couple of changes
● Inter-developer duplication
○ Make it easy to use/reuse
Clean code
Don’t Repeat Yourself (DRY)

● Imposed duplication (unavoidable case)
○ Multiple representations of information
● Use a copy-paste detector
Clean code
Don’t Repeat Yourself (DRY)

● The less, the better!
● Usually comments are not needed
○ Redundant
○ Outdated
● Or even worse..
○ Commented out code
Clean code
Comments

Clean code
Any useful comment here?
class FeedParser
{
{
$products = array(); //array of products to return
$xml = simplexml_load_file("/tmp/products.xml"); //read xml file
throw new Exception("feed not found"); //file not found
} else {
} else {
$prod = $this->parse_elem($elem);
array_push($products, $prod); //add Product object
}
}
}
return $products;
}
(...)

● Use the code itself to explain the logic
○ Use a variable instead of a comment
○ Use intention revealing names in vars and functions
Clean code
Comments

Clean code
Use a variable instead of a comment
{
}

Clean code
Use a variable instead of a comment
{
}
--------
{
$isActive = false;
return new Product($name, $url, $elem->id, $isActive);
}

● Intention-revealing names
○ int days; //days since last purchase
○ int daysSinceLastPurchase;
● Shared vocabulary with the team
● Precise vocabulary
○ No “manageUser(...)” but “updateUserContactInfo(...)”
○ No “killUserInDb()” but “deleteUserFromDb()”
Clean code
Naming

Clean code
Looking for meaningful names
{
$isActive = false;
}

Clean code
Looking for meaningful names
{
$isActive = false;
}
--------
private function createProductFromXmlData($productXmlData)
{
$name = $this->getAttribute($productXmlData, "title");
$url = $this->getAttribute($productXmlData, "link");
$isActive = false;
return new Product($name, $url, $productXmlData->id, $isActive);
}

● Small! Really small!
○ 2, 3, 4 lines
● Do ONLY one thing!
Clean code
Easier functions

Clean code
Does doParse() do only one thing?
{
$products = array();
$xml = simplexml_load_file("/tmp/products.xml");
throw new Exception("feed not found");
} else {
} else {
$prod = $this->createProductFromXmlData($elem);
array_push($products, $prod);
}
}
}
return $products;
}

Clean code
{
$xmlData = $this->readXML("/tmp/products.xml");
$products = $this->extractProductsFromXmlData($xmlData);
return $products;
}
private function readXML($filename)
{
$xmlData = simplexml_load_file($filename);
if ($xmlData === FALSE) {
} elseif (count($xml) === 0) {
}
return $xmlData;
}
private function extractProductsFromXmlData($xmlData)
{
$products = array();
foreach($xmlData as $productXml) {
$prod = $this->createProductFromXmlData($productXml);
array_push($products, $prod);
}
return $products;
}

● Keep same level of abstraction
○ From top to bottom, outside in
● Arguments
○ Avoid many arguments: use objects or DTOs instead
○ Caution with flags (bool arguments)
Clean code
Easier functions

Clean code
Avoiding flags, and keeping same level
{
$isActive = false;
}

Clean code
Avoiding flags, and keeping same level
{
$isActive = false;
}
{
$id = $this->getAttribute($productXmlData, "id");
return new Product::createInactive($name, $url, $id);
}

● Guard clauses
● Configuration over hardcoding
Clean code
Cleaner logic

Clean code
{
}
return $xmlData;
}
// Let’s add guard clauses

Clean code
{
}
return $xmlData;
}
// Let’s add guard clauses
{
$this->checkFileExists($filename);
$this->checkXmlHasContent($xmlData);
return $xmlData;
}
private function checkFileExists($filename)
{
if (!file_exists($filename)) {
throw new Exception("File $filename not found");
}
}

Clean code
class FeedParser
{
{
return $products;
}
// Let’s remove the hardcoding

Clean code
class FeedParser
{
{
return $products;
}
// Let’s remove the hardcoding
class FeedParser
{
public function __construct($filename)
{
$this->XmlFilename = $filename;
}
{
$xmlData = $this->readXML($this->XmlFilename);
return $products;
}

● Books:
○ Clean Code (Robert “Uncle Bob” Martin)
○ The Pragmatic Programmer (Hunt & Tomas)
○ Refactoring (Fowler)
Clean code
And you can continue cleaning… forever

Introduction to Clean Code

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