2. Who am I?
• Dagfinn Reiersøl
– dagfinn@reiersol.com
– Twitter: @dagfinnr
– Blog: agilephp.com
• Mostly PHP since 1999
• Wrote PHP in Action
• Code quality / agile development enthusiast
Dagfinn Reiersøl, ABC Startsiden 2
3. What is a code smell?
Train your nose to tell you...
– ...when to refactor
– ...what to refactor
– ...how to refactor
Dagfinn Reiersøl, ABC Startsiden 3
4. It's more like a diagnosis
• A disease has a treatment, a code smell has a refactoring
• (or several)
• Code smell distinctons are important
• For each smell, there is one or more refactorings
• http://industriallogic.com/papers/smellstorefactorings.pdf
Dagfinn Reiersøl, ABC Startsiden 4
5. What is refactoring?
• “Improving the design of existing code”
• Maintain behavior
• Change the structure
• Make it more readable, eliminate duplication
• Proceed by small steps
• Keep code working always
Dagfinn Reiersøl, ABC Startsiden 5
6. The “bible” of refactoring
• “Martin Fowler...is not Jesus
Christ, and his books are not
the Bible.”
• Except this one really is the
bible.
• Java examples, but mostly
PHP-relevant
Dagfinn Reiersøl, ABC Startsiden 6
7. Refactoring is a specific,
learnable skill
• Learn to apply specific, named refactorings.
• Refactorings have specific instructions
• Learn to go in baby steps
• Test between each step
• Undo if you get lost
• Weird intermediate results are OK
Dagfinn Reiersøl, ABC Startsiden 7
8. Refactoring in PHP
• Very little tool support
• This is both a bad thing and a good thing
• Extract Method is particularly crucial, but unsupported by tools
Dagfinn Reiersøl, ABC Startsiden 8
9. Why refactor?
• Make code easier to read (saves time)
• Make it easier to find bugs
• Learn design principles
• Discover new abstractions
• Clean, maintainable code
Dagfinn Reiersøl, ABC Startsiden 9
10. How much is enough?
• Make it as clean as you possibly can, if circumstances allow
• Boy Scout Rule
• When you change code, you're likely to change it again soon
• Better code needs less refactoring
• Better code is easier to refactor
Dagfinn Reiersøl, ABC Startsiden 10
11. Why duplication is so bad
• Harder to maintain
• Harder to debug
• Incomplete bug fixes
Original code Original code
First copy Debug First copy
Second copy Second copy
Dagfinn Reiersøl, ABC Startsiden 11
12. Automated test coverage is
essential
• Unit tests primarily
• Tests make it easy to fix when you break something
• Acceptance tests helpful sometimes
• Manual testing only in special, desperate circumstances
• Legacy code paradox
Dagfinn Reiersøl, ABC Startsiden 12
13. Another bible: Clean Code
• Lots of smells and
heuristics
Dagfinn Reiersøl, ABC Startsiden 13
14. Don't take examples personally
• I'm using somewhat real open-source examples
• No personal criticism implied
• Refactoring examples must be somewhere in the middle (not
awful, not perfect)
• Awful is too hard to refactor (=advanced material)
• Perfect doesn't exist
• Just pretend I wrote all of it ;-)
Dagfinn Reiersøl, ABC Startsiden 14
15. Duplicated Code
// even if we are interacting between a table defined in a
// class and a/ table via extension, ensure to persist the
// definition
if (($tableDefinition = $this->_table->getDefinition()) !== null
&& ($dependentTable->getDefinition() == null)) {
$dependentTable->setOptions(
array(Table::DEFINITION => $tableDefinition));
}
...
// even if we are interacting between a table defined in a
// class and a/ table via extension, ensure to persist the
// definition
Dagfinn Reiersøl, ABC Startsiden= $this->_table->getDefinition()) !== 15
if (($tableDefinition null
16. Long Method
• Long methods are evil
• Hard to read (time-consuming)
• Hard to test
• Tend to have duplicate logic
• Hard to override specific behaviors
Dagfinn Reiersøl, ABC Startsiden 16
17. How long?
• “The first rule of functions is that they should be small”
• “The second rule of functions is that they should be smaller than
that”. - Robert C. Martin, Clean Code
• My experience: the cleanest code has mostly 2-5 line methods
• But don't do it if it doesn't make sense
• Do One Thing
• One level of abstraction only
Dagfinn Reiersøl, ABC Startsiden 17
18. Refactoring a Long Method
• Split method into smaller methods
• Extract Method is the most important refactoring
// Execute cascading updates against dependent tables.
// Do this only if primary key value(s) were changed.
if (count($pkDiffData) > 0) {
$depTables = $this->_getTable()->getDependentTables();
if (!empty($depTables)) {
$pkNew = $this->_getPrimaryKey(true);
$pkOld = $this->_getPrimaryKey(false);
foreach ($depTables as $tableClass) {
$t = $this->_getTableFromString($tableClass);
$t->_cascadeUpdate($this->getTableClass(),
$pkOld, $pkNew);
}
}
Dagfinn Reiersøl, ABC Startsiden 18
19. Extract Method: mechanics
1.Copy the code into a new method
2.Find all temporary variables
3.Return all of them from the method
In PHP, unlike Java, we can return multiple variabless
4.Find the ones that are initialized in the method
5.Pass all of those into the method
6.The result is ugly, but a step forward
Dagfinn Reiersøl, ABC Startsiden 19
20. Extract Method: result
private function executeCascadingUpdates($pkDiffData) {
if (count($pkDiffData) > 0) {
$depTables = $this->_getTable()->getDependentTables();
if (!empty($depTables)) {
$pkNew = $this->_getPrimaryKey(true);
$pkOld = $this->_getPrimaryKey(false);
foreach ($depTables as $tableClass) {
$t = $this->_getTableFromString($tableClass);
$t->_cascadeUpdate(
$this->getTableClass(), $pkOld, $pkNew);
}
}
}
return array($pkDiffData,$tableClass,
$depTables,$pkNew,$pkOld,$t);
}
Dagfinn Reiersøl, ABC Startsiden 20
21. Validation Overcrowding
function setTable(Table $table){
$tableClass = get_class($table);
if (! $table instanceof $this->_tableClass) {
require_once 'My_Exception.php';
throw new My_exception("blah blah");
}
$this->_table = $table;
$this->_tableClass = $tableClass;
$info = $this->_table->info();
if ($info['cols'] != array_keys($this->_data)) {
require_once 'My_Exception.php';
throw new My_exception("blah blah");
}
if (!array_intersect((array)$this->_primary, info['primary'])
== (array) $this->_primary) {
require_once 'My_Exception.php';
throw new My_exception("blah blah");
}
$this->_connected = true;
Dagfinn Reiersøl, ABC Startsiden 21
22. Extracting Validation
• Don't waste time reading validation code
• Extract validation (logging, error handling) into separate
method(s)
function setTable(Table $table) {
$this-validateTable($table);
$this->_table = $table;
$this->_tableClass = get_class($table);
$this->_connected = true;
}
Dagfinn Reiersøl, ABC Startsiden 22
23. Large Class
• As methods get smaller, there will be more of them
• Hard to keep track of all the methods
• Class has multiple responsibilities
• A class should have only one reason to change
• Duplication is likely
Dagfinn Reiersøl, ABC Startsiden 23
24. Refactoring a Large Class
• Primarily Extract Class
• Look for patterns in method names
function __construct($url = null, $useBrackets = true)...
function initialize()...
function getURL()...
function addQueryString($name, $value, $preencoded = false)...
function removeQueryString($name)...
function addRawQueryString($querystring)...
function getQueryString()...
function _parseRawQuerystring($querystring)...
function resolvePath($path)...
function getStandardPort($scheme)...
function setProtocol($protocol, $port = null)...
function setOption($optionName, $value)...
function getOption($optionName)...
Dagfinn Reiersøl, ABC Startsiden 24
25. Refactoring a Large Class
• Look for
– Patterns in method names (see previous)
– Subset of data and methods that go together
– Subset of data that change together
• Mechanics in short
– Create a new class
– Copy variables and methods into it
– Change methods one by one to delegate to the new class
• You must have automated tests
Dagfinn Reiersøl, ABC Startsiden 25
26. Primitive Obsession
“People new to objects usually are reluctant to use small objects
for small tasks, such as money classes that combine number
and currency, ranges with an upper and lower, and special
strings such as telphone numbers and ZIP codes.”
- Martin Fowler, Refactoring
Dagfinn Reiersøl, ABC Startsiden 26
27. Primitive obsession: non-OO
dates
• Will this work?
strftime($arrivaltime);
• Plain PHP date handling is ambiguous, obscure and error-prone
• Use objects instead
$datetime = new DateTime('2008-08-03 14:52:10');
echo $datetime->format('jS, F Y') . "n";
Dagfinn Reiersøl, ABC Startsiden 27
28. Primitive obsession example
• The primary key is an array (when?) or a scalar (when?)
• Are these names or values?
if (is_array($primaryKey)) {
$newPrimaryKey = $primaryKey;
} else {
$tempPrimaryKey = (array) $this->_primary;
$newPrimaryKey = array(
current($tempPrimaryKey) => $primaryKey);
}
return $newPrimaryKey;
Dagfinn Reiersøl, ABC Startsiden 28
29. Primitive obsession example
• Huh?
/**
* Were any of the changed columns part of the primary key?
*/
$pkDiffData = array_intersect_key(
$diffData, array_flip((array)$this->_primary));
}
• It's clever, obscure, therefore error-prone
• I think I prefer this:
foreach ((array)$this->_primary as $pkName) {
if (array_key_exists($pkName,$diffData))
$pkDiffData[$pkName] = $diffData[$pkName];
}
Dagfinn Reiersøl, ABC Startsiden 29
30. Primary key class
class PrimaryKey {
public function __construct($primitive) {
$this->primitive = $primitive;
}
public function isCompoundKey() {
return is_array($this->primitive);
}
public function getSequenceColumn() {
return array_shift($this->asArray());
}
public function asArray() {
return (array) $this->primitive;
}
public function filter($data) {
return array_intersect_key(
$data, array_flip($this->asArray()));
}
}
Dagfinn Reiersøl, ABC Startsiden 30
31. Benefits of the PrimaryKey class
• More expressive client code
• Details can be found in one place
• Less duplication
• Easier to add features
• Much easier to test
Dagfinn Reiersøl, ABC Startsiden 31
32. More expressive code and tests
• What this comment is telling us...
/**
* [The class] assumes that if you have a compound primary key
* and one of the columns in the key uses a sequence,
* it's the _first_ column in the compound key.
*/
• ...can be expressed as a test.
/** @test */
function shouldAssumeFirstColumnIsSequenceColumn() {
$primaryKey = new PrimaryKey('phone','name');
$this->assertEquals(
'phone',
$primaryKey->getSequenceColumn()
);
}
Dagfinn Reiersøl, ABC Startsiden 32
33. Consider a small class when...
• ...two or more data values occur together repeatedly (ranges,
etc)
• ...you keep testing the type of a data value
• ...you keep converting a data value
• ...you keep testing for null
Dagfinn Reiersøl, ABC Startsiden 33
35. Don't return null
Alternatives:
• Throw an exception
• Return an empty array
• Return a Null Object (Special Case)
Dagfinn Reiersøl, ABC Startsiden 35
36. Nested ifs and loops
• Hard to read
• Even harder to test
if (isset($this->session)) {
//...
if (isset($this->session['registered'])
&& isset($this->session['username'])
&& $this->session['registered'] == true
&& $this->session['username'] != '') {
//...
if ($this->advancedsecurity) {
$this->log(
'Advanced Security Mode Enabled.',AUTH_LOG_DEBUG);
//...
Dagfinn Reiersøl, ABC Startsiden 36
37. How to deal with nesting
• Start with the deepest level, extract methods
• How much code to extract?
– Whole expression (foreach (...) {...})
– Code inside expression
– Part of code inside expression
• Adding tests (if none exist)
– Write tests first, then extract?
– Or do careful extraction, then add tests?
• Replace Nested Conditional with Guard Clauses
Dagfinn Reiersøl, ABC Startsiden 37
38. Conditionals in general
• Often smelly
• Learn how to avoid or simplify them
• http://www.antiifcampaign.com
• Replace Conditional with Polymorphism
• Decompose Conditional
// handle single space character
if(($nb==1) AND preg_match("/[s]/u", $s))
if($this->isSingleSpaceCharacter($s))
Dagfinn Reiersøl, ABC Startsiden 38
39. Feature envy / Inappropriate
Intimacy
• Does the row object need to poke inside the table objects,
checking for null?
• No, it's an implementation detail of the Table class
• It's accessed as if it were public, breaking encapsulation
abstract class Row...
if (($tableDefinition = $this->_table->getDefinition())
!== null
&& ($dependentTable->getDefinition() == null))
{
$dependentTable->setOptions(
Dagfinn Reiersøl, ABC Startsiden
array(Table::DEFINITION 39
40. Move everything into the
“envied” class?
This simple?
$dependentTable->copyDefinitionFrom($this->_table);
Misleading method name. How about this?
$dependentTable->copyDefinitionIfNeededFrom($this->_table);
Ugh. Let's Separate Query from Modifier
if (!$dependentTable->hasDefinition()) //query
$dependentTable->copyDefinitionFrom($this->_table);
Dagfinn Reiersøl, ABC Startsiden 40
41. Redundant Comment
/**
* If the _cleanData array is empty,
* this is an INSERT of a new row.
* Otherwise it is an UPDATE.
*/
if (empty($this->_cleanData)) {
return $this->_doInsert();
} else {
return $this->_doUpdate();
}
Dagfinn Reiersøl, ABC Startsiden 41
42. (Partly) obsolete comment
The comment has (apparently) not been updated to include all
options
* Supported params for $config are:-
* - table...
* - data...
* @param...
public function __construct(array $config = array())...
{
if (isset($config['table'])...
if (isset($config['data']))...
Dagfinn Reiersøl, ABC Startsiden 42
if (isset($config['stored'])...
43. Functions should descend only one
level of abstraction
• _cleanData is at a lower level of abstraction than _doInsert()
and _doUpdate()
• This is hard, but important
if (empty($this->_cleanData)) {
return $this->_doInsert();
} else {
return $this->_doUpdate();
}
if ($this->isNewObject()) {
return $this->_doInsert();
} else {
return $this->_doUpdate();
}
Dagfinn Reiersøl, ABC Startsiden 43
44. Long Parameter List
• Hard-to-read method calls, especially with nulls and booleans
• Uncle Bob: More than three arguments “require special
justification”
• Easy to mix up arguments, causing bugs
• Hard to test all variations
$nextContent = $phpcsFile->findNext(
array(T_WHITESPACE, T_COMMENT),
($closeBrace + 1), null, true
);
Dagfinn Reiersøl, ABC Startsiden 44
45. One way to shrink the argument
list
• Remove unused arguments
public function quoteInto($text, $value,
$type = null, $count = null)
Dagfinn Reiersøl, ABC Startsiden 45
46. Replace optional / boolean
arguments with methods
Boolean argument
protected function _getPrimaryKey($useDirty = true)
Split into separate methods instead
protected function _getPrimaryKeyDirty()
protected function _getPrimaryKeyClean()
Or even objects
$this->dirtyData->getPrimaryKey();
$this->cleanData->getPrimaryKey();
Dagfinn Reiersøl, ABC Startsiden 46
47. Introduce Parameter Object
• Encapsulate two or more arguments in a class
• Try to make it more meaningful than “options”
public function log($id, $username, $command = 'unknown',
$action,$e)
public function log(LogEvent $event)...
Dagfinn Reiersøl, ABC Startsiden 47