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Looping the Loop with SPL Iterators

The document discusses iterators in PHP. It explains that an iterator is an object that enables traversing a container, especially lists. It describes different types of iterables like arrays, iterators, generators, and iterator aggregates. It shows how to implement an iterator by having a class implement the Iterator interface and its methods. It also provides examples of implementing iterators to iterate over strings, file lines, and database results. The document discusses different standard PHP library iterators like ArrayIterator and how ArrayIterator also implements interfaces like Countable.

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Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators What is an Iterator? An Iterator is an object that enables a programmer to traverse a container, particularly lists. A Behavioural Design Pattern (GoF)
Looping the Loop with SPL Iterators What is an Iterator? $dataSet = ['A', 'B', 'C']; foreach($dataSet as $key => $value) { echo "{$key} => {$value}", PHP_EOL; }
Looping the Loop with SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
Looping the Loop with SPL Iterators What is an Iterator? $data = ['A', 'B', 'C']; $dataSet = new ArrayIterator($data); foreach($dataSet as $key => $value) { echo "{$key} => {$value}", PHP_EOL; }
Looping the Loop with SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
Looping the Loop with SPL Iterators What is an Iterator? interface Iterator extends Traversable { /* Methods */ abstract public current ( void ) : mixed abstract public key ( void ) : scalar abstract public next ( void ) : void abstract public rewind ( void ) : void abstract public valid ( void ) : bool }
Looping the Loop with SPL Iterators What is an Iterator? $data = ['A', 'B', 'C']; $iterator = new ArrayIterator($data); $iterator->rewind(); while ($iterator->valid()) { $key = $iterator->key(); $value = $iterator->current(); echo "{$key} => {$value}", PHP_EOL; $iterator->next(); }
Looping the Loop with SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate
Looping the Loop with SPL Iterators The Iterable Tree Not all iterables are equal You can count the elements in an array ! Can you count the elements in an Iterator?
Looping the Loop with SPL Iterators The Iterable Tree Not all iterables are equal You can access the elements of an array by their index ! Can you access the elements of an Iterator by index ?
Looping the Loop with SPL Iterators The Iterable Tree Not all iterables are equal You can rewind an Iterator ! Can you rewind a Generator ?
Looping the Loop with SPL Iterators The Iterable Tree Not all iterables are equal Iterator_* functions (e.g. iterator_to_array) work on Iterators ? Can you use iterator_* functions on an IteratorAggregate ?
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Iterable is a pseudo-type introduced in PHP 7.1. It accepts any array, or any object that implements the Traversable interface. Both of these types are iterable using foreach.
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate An array in PHP is an ordered map, a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and more. The foreach control structure exists specifically for arrays.
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Abstract base interface to detect if a class is traversable using foreach. It cannot be implemented alone in Userland code; but instead must be implemented through either IteratorAggregate or Iterator. Internal (built-in) classes that implement this interface can be used in a foreach construct and do not need to implement IteratorAggregate or Iterator.
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Abstract base interface to detect if a class is traversable using foreach. It cannot be implemented alone in Userland code; but instead must be implemented through either IteratorAggregate or Iterator. PDOStatement DatePeriod SimpleXMLElement
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate An Interface for external iterators or objects that can be iterated themselves internally. PHP already provides a number of iterators for many day to day tasks within the Standard PHP Library (SPL). SPL Iterators SPL DataStructures WeakMaps (PHP 8)
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Generators provide an easy way to implement simple user-defined iterators without the overhead or complexity of implementing a class that implements the Iterator interface. This flexibility does come at a cost, however: generators are forward-only iterators, and cannot be rewound once iteration has started.
Looping the Loop with SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate IteratorAggregate is a special interface for implementing an abstraction layer between user code and iterators. Implementing an IteratorAggregate will allow you to delegate the work of iteration to a separate class, while still enabling you to use the collection inside a foreach loop.
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators Implementing an Iterator interface Iterator extends Traversable { /* Methods */ abstract public current ( void ) : mixed abstract public key ( void ) : scalar abstract public next ( void ) : void abstract public rewind ( void ) : void abstract public valid ( void ) : bool }
Looping the Loop with SPL Iterators Implementing an Iterator class Utf8StringIterator implements Iterator { private $string; private $offset = 0; private $length = 0; public function __construct(string $string) { $this->string = $string; $this->length = iconv_strlen($string); } public function valid(): bool { return $this->offset < $this->length; } ... }
Looping the Loop with SPL Iterators Implementing an Iterator class Utf8StringIterator implements Iterator { ... public function rewind(): void { $this->offset = 0; } public function current(): string { return iconv_substr($this->string, $this->offset, 1); } public function key(): int { return $this->offset; } public function next(): void { ++$this->offset; } }
Looping the Loop with SPL Iterators Implementing an Iterator $stringIterator = new Utf8StringIterator('Καλησπέρα σε όλους'); foreach($stringIterator as $character) { echo "[{$character}]"; }
Looping the Loop with SPL Iterators Implementing an Iterator [Κ][α][λ][η][σ][π][έ][ρ][α][ ][σ][ε][ ][ό][λ][ο][υ][ς]
Looping the Loop with SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { private $fileHandle; private $line = 1; public function __construct(string $fileName) { $this->fileHandle = fopen($fileName, 'r'); } public function __destruct() { fclose($this->fileHandle); } }
Looping the Loop with SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { ... public function current(): string { $fileData = fgets($this->fileHandle); return rtrim($fileData, "n"); } public function key(): int { return $this->line; } public function next(): void { ++$this->line; } }
Looping the Loop with SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { ... public function rewind(): void { fseek($this->fileHandle, 0); $this->line = 1; } public function valid(): bool { return !feof($this->fileHandle); } }
Looping the Loop with SPL Iterators Implementing an Iterator $fileLineIterator = new FileLineIterator(__FILE__); foreach($fileLineIterator as $lineNumber => $fileLine) { echo "{$lineNumber}: {$fileLine}", PHP_EOL; }
Looping the Loop with SPL Iterators Implementing an Iterator 1: <?php 2: 3: class FileLineIterator implements Iterator { 4: private $fileHandle; 5: private $line = 1; 6: 7: public function __construct(string $fileName) { 8: $this->fileHandle = fopen($fileName, 'r’); 9: } 10: …
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): array { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return array_map(fn(array $user): User => User::fromArray($user), $users); } }
Looping the Loop with SPL Iterators class UserRepository { // ... /** * @return User[] */ public function all(): array { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return array_map(fn(array $user): User => User::fromArray($user), $users); } }
Looping the Loop with SPL Iterators class UserCollection extends ArrayIterator { }
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection( array_map(fn(array $user): User => User::fromArray($user), $users) ); } }
Looping the Loop with SPL Iterators class UserCollection extends ArrayIterator { public function current(): User { return User::fromArray(parent::current()); } }
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection($users); } }
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator)
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable
Looping the Loop with SPL Iterators ArrayIterator – Countable interface Countable { /* Methods */ abstract public count ( void ) : int }
Looping the Loop with SPL Iterators ArrayIterator – Countable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userCount = count($userList); echo "There are {$userCount} users in this list", PHP_EOL;
Looping the Loop with SPL Iterators ArrayIterator – Countable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); echo "There are {$userList->count()} users in this list", PHP_EOL;
Looping the Loop with SPL Iterators ArrayIterator – Countable There are 4 users in this list
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable ArrayAccess
Looping the Loop with SPL Iterators ArrayIterator – ArrayAccess interface ArrayAccess { /* Methods */ abstract public offsetExists ( mixed $offset ) : bool abstract public offsetGet ( mixed $offset ) : mixed abstract public offsetSet ( mixed $offset , mixed $value ) : void abstract public offsetUnset ( mixed $offset ) : void }
Looping the Loop with SPL Iterators ArrayIterator – ArrayAccess $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); echo "The 3rd entry in the list is {$userList[2]}", PHP_EOL;
Looping the Loop with SPL Iterators ArrayIterator – ArrayAccess The 3rd entry in the list is user3
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable
Looping the Loop with SPL Iterators ArrayIterator – Serializable interface Serializable { /* Methods */ abstract public serialize ( void ) : string abstract public unserialize ( string $serialized ) : void }
Looping the Loop with SPL Iterators ArrayIterator – Serializable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); var_dump(serialize($userList));
Looping the Loop with SPL Iterators ArrayIterator – Serializable string(117) "O:8:"UserList":4:{i:0;i:0;i:1;a:4:{i:0;s:5:"user1"; i:1;s:5:"user2";i:2;s:5:"user3";i:3;s:5:"user4";}i:2; a:0:{}i:3;N;}"
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator)
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator SeekableIterator extends Iterator { /* Methods */ abstract public seek ( int $position ) : void /* Inherited methods */ abstract public Iterator::current ( void ) : mixed abstract public Iterator::key ( void ) : scalar abstract public Iterator::next ( void ) : void abstract public Iterator::rewind ( void ) : void abstract public Iterator::valid ( void ) : bool }
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userList->seek(2); while ($userList->valid()) { echo $userList->current(), PHP_EOL; $userList->next(); }
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator user3 user4
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userList->seek(2); foreach($userList as $userName) { echo $userName, PHP_EOL; }
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator user1 user2 user3 user4 
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator $userData = ['A' => 'user1', 'B' => 'user2', 'C' => 'user3', 'D' => 'user4']; $userList = new UserList($userData); $userList->seek('C'); while ($userList->valid()) { echo $userList->current(), PHP_EOL; $userList->next(); }
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator PHP7 Warning: ArrayIterator::seek() expects parameter 1 to be int, string given 
Looping the Loop with SPL Iterators ArrayIterator – SeekableIterator PHP8 Fatal error: Uncaught TypeError ArrayIterator::seek(): Argument #1 ($position) must be of type int, string given 
Looping the Loop with SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator) Also provides methods for sorting Doesn’t work with array_* functions
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators LimitIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new LimitIterator( new UserList($userData), 2, 1 ); foreach($userList as $value) { echo $value, PHP_EOL; }
Looping the Loop with SPL Iterators LimitIterator user3
Looping the Loop with SPL Iterators InfiniteIterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-08'))->format('w'); $weekdayList = new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ); foreach($weekdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
Looping the Loop with SPL Iterators InfiniteIterator Tues Wed Thurs Fri Sat Sun Mon Tues Wed Thurs Fri Sat Sun Mon
Looping the Loop with SPL Iterators CallbackFilterIterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-15'))->format('w'); $workdayList = new CallbackFilterIterator( new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ), fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
Looping the Loop with SPL Iterators CallbackFilterIterator Tues Wed Thurs Fri Mon Tues Wed Thurs Fri Mon
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators FilterIterator abstract FilterIterator extends IteratorIterator implements OuterIterator { /* Methods */ public abstract accept ( void ) : bool public __construct ( Iterator $iterator ) public current ( void ) : mixed public getInnerIterator ( void ) : Iterator public key ( void ) : mixed public next ( void ) : void public rewind ( void ) : void public valid ( void ) : bool }
Looping the Loop with SPL Iterators FilterIterator class ImageFileIterator extends FilterIterator { // Overwrite the constructor to automagically create an inner iterator // to iterate the file system when given a path name. public function __construct(string $path) { parent::__construct(new FilesystemIterator($path)); } // Overwrite the accept method to perform a super simple test to // determine if the files found were images or not. public function accept(): bool { $fileObject = $this->getInnerIterator()->current(); return preg_match('/^(?:gif|jpe?g|png)$/i', $fileObject->getExtension()); } }
Looping the Loop with SPL Iterators FilterIterator class ImageFileIterator extends FilterIterator { // Overwrite the constructor to automagically create an inner iterator // to iterate the file system when given a path name. public function __construct(string $path) { parent::__construct(new FilesystemIterator($path)); } // Overwrite the accept method to perform a super simple test to // determine if the files found were images or not. public function accept(): bool { return preg_match('/^(?:gif|jpe?g|png)$/i', $this->getExtension()); } }
Looping the Loop with SPL Iterators FilterIterator $path = dirname(__FILE__); foreach(new ImageFileIterator($path) as $imageObject) { echo $imageObject->getBaseName(), PHP_EOL; }
Looping the Loop with SPL Iterators FilterIterator anubis.jpg Carpet.jpg Crazy Newspaper Headlines.jpg elephpant.jpg Pie Chart.jpg PowerOfBooks.jpg Struggling-Team.png TeddyBears.jpg
Looping the Loop with SPL Iterators Iterator Keys class ImageFileIterator extends FilterIterator { ... // Overwrite the key method to return the file extension as the key public function key(): string { return $this->getExtension(); } } foreach(new ImageFileIterator($path) as $extension => $imageObject) { echo "{$extension} => {$imageObject->getBaseName()}", PHP_EOL; }
Looping the Loop with SPL Iterators Iterator Keys jpg => anubis.jpg jpg => Carpet.jpg jpg => Crazy Newspaper Headlines.jpg jpg => elephpant.jpg jpg => Pie Chart.jpg jpg => PowerOfBooks.jpg png => Struggling-Team.png jpg => TeddyBears.jpg
Looping the Loop with SPL Iterators Iterator Keys class ImageFileIterator extends FilterIterator { ... // Overwrite the key method to return the last modified date/time as the key public function key(): DateTime { return DateTime::createFromFormat('U', $this->getMTime()); } } foreach(new ImageFileIterator($path) as $date => $imageObject) { echo "{$date->format('Y-m-d H:i:s')} => {$imageObject->getBaseName()}", PHP_EOL; }
Looping the Loop with SPL Iterators Iterator Keys 2012-03-24 00:38:24 => anubis.jpg 2013-01-27 22:32:20 => Carpet.jpg 2013-03-07 12:16:24 => Crazy Newspaper Headlines.jpg 2012-02-16 22:31:56 => elephpant.jpg 2012-10-09 11:51:56 => Pie Chart.jpg 2012-07-17 12:22:32 => PowerOfBooks.jpg 2012-12-30 18:14:24 => Struggling-Team.png 2012-01-31 11:17:32 => TeddyBears.jpg
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators MultipleIterator $dates = ['Q1-2019', 'Q2-2019', 'Q3-2019', 'Q4-2019']; $budget = [1200, 1300, 1400, 1500]; $expenditure = [1250, 1315, 1440, 1485]; $budgetElements = count($budget); for ($i = 0; $i < $budgetElements; $i++) { echo "{$dates[$i]} - {$budget[$i]}, {$expenditure[$i]}", PHP_EOL; }
Looping the Loop with SPL Iterators MultipleIterator $dates = ['Q1-2019', 'Q2-2019', 'Q3-2019', 'Q4-2019']; $budget = [1200, 1300, 1400, 1500]; $expenditure = [1250, 1315, 1440, 1485]; foreach($dates as $key => $period) { echo "{$period} - {$budget[$key]}, {$expenditure[$key]}", PHP_EOL; }
Looping the Loop with SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
Looping the Loop with SPL Iterators MultipleIterator function wrapArrayAsIterator(array $array) { return new ArrayIterator($array); } $combinedIterable = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $combinedIterable->attachIterator(wrapArrayAsIterator($dates), 'date'); $combinedIterable->attachIterator(wrapArrayAsIterator($budget), 'budget'); $combinedIterable->attachIterator(wrapArrayAsIterator($expenditure), 'expenditure');
Looping the Loop with SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { echo $dateValues['date'], " - {$dateValues['budget']}, {$dateValues['expenditure']}", PHP_EOL; }
Looping the Loop with SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { [$date, $budget, $expenditure] = $dateValues; echo "{$date} - {$budget}, {$expenditure}", PHP_EOL; }
Looping the Loop with SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
Looping the Loop with SPL Iterators MultipleIterator function wrapArrayAsIterator(array $array) { return new ArrayIterator($array); } $combinedIterable = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $combinedIterable->attachIterator(wrapArrayAsIterator($dates), 'date'); $combinedIterable->attachIterator(wrapArrayAsIterator($budget), 'budget'); $combinedIterable->attachIterator(wrapArrayAsIterator($expenditure), 'expenditure');
Looping the Loop with SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { extract($dateValues); echo "{$date} - {$budget}, {$expenditure}", PHP_EOL; }
Looping the Loop with SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
Looping the Loop with SPL Iterators MultipleIterator $allocations = $totalAdvance->allocateTo(count($cars)); foreach ($cars as $i => $car) { $car->setAdvance($allocations[$i]); }
Looping the Loop with SPL Iterators MultipleIterator $allocations = $totalAdvance->allocateTo(count($cars)); $advanceAllocations = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $advanceAllocations->attachIterator(ArrayIterator($cars), 'car'); $advanceAllocations->attachIterator(ArrayIterator($allocations), 'advance'); foreach($advanceAllocations as $advanceAllocation) { extract($advanceAllocation); $car->setAdvance($advance); }
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators Inner and Outer Iterators Inner Iterator Implements Iterator, or extends a class that implements Iterator ArrayIterator SeekableIterator FilesystemIterator MultipleIterator
Looping the Loop with SPL Iterators Inner and Outer Iterators Outer Iterator Implements OuterIterator, or extends an Iterator that already implements OuterIterator LimitIterator InfiniteIterator FilterIterator CallbackFilterIterator
Looping the Loop with SPL Iterators Recursive Iterators A RecursiveIterator defines methods to allow iteration over hierarchical data structures. Nested Arrays (and Objects if using ArrayAccess) Filesystem Directories/Folders
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection( array_map(fn(array $user): User => User::fromArray($user), $users) ); } }
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): Generator { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); while ($user = $statement->fetch()) { yield User::fromArray($user); } } }
Looping the Loop with SPL Iterators class UserRepository { // ... /** * @return Generator|User[] */ public function all(): Generator { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); while ($user = $statement->fetch()) { yield User::fromArray($user); } } }
Looping the Loop with SPL Iterators IteratorAggregate IteratorAggregate extends Traversable { /* Methods */ abstract public getIterator ( void ) : Traversable }
Looping the Loop with SPL Iterators class UserCollection implements IteratorAggregate { private PDOStatement $pdoStatement; public function __construct(PDOStatement $pdoStatement) { $this->pdoStatement = $pdoStatement; } public function getIterator(): Traversable { $this->pdoStatement->execute(); while ($user = $this->pdoStatement->fetch()) { yield User::fromArray($user); } } }
Looping the Loop with SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); return new UserCollection($statement); } }
Looping the Loop with SPL Iterators Implementing a Fluent Nested Iterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-15'))->format('w'); $workdayList = new CallbackFilterIterator( new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ), fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
Looping the Loop with SPL Iterators Implementing a Fluent Nested Iterator class FluentNestedIterator implements IteratorAggregate { protected iterable $iterator; public function __construct(iterable $iterator) { $this->iterator = $iterator; } public function with(string $iterable, ...$args): self { $this->iterator = new $iterable($this->iterator, ...$args); return $this; } public function getIterator() { return $this->iterator; } }
Looping the Loop with SPL Iterators Implementing a Fluent Nested Iterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-10-08'))->format('w'); $workdayList = (new FluentNestedIterator(new ArrayIterator($weekdayNames))) ->with(InfiniteIterator::class) ->with(LimitIterator::class, $todayOffset, 14) ->with( CallbackFilterIterator::class, fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
Looping the Loop with SPL Iterators Implementing a Fluent Nested Iterator Thurs Fri Mon Tues Wed Thurs Fri Mon Tues Wed
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators Array Functions Don’t work with Traversables
Looping the Loop with SPL Iterators Array Functions Don’t work with Traversables
Looping the Loop with SPL Iterators Array Functions – Filter function filter(iterable $iterator, Callable $callback = null) { if ($callback === null) { $callback = 'iterableFilterNotEmpty'; } foreach ($iterator as $key => $value) { if ($callback($value)) { yield $key => $value; } } }
Looping the Loop with SPL Iterators Array Functions – Filter $startTime = new DateTime('2015-11-23 13:20:00Z'); $endTime = new DateTime('2015-11-23 13:30:00Z'); $timeFilter = function($timestamp) use ($startTime, $endTime) { return $timestamp >= $startTime && $timestamp <= $endTime; }; $filteredTrackingData = filter( $gpxReader->getElements('trkpt'), $timeFilter, ARRAY_FILTER_USE_KEY ); foreach ($filteredTrackingData as $time => $element) { ... }
Looping the Loop with SPL Iterators Array Functions – Filter 2015-11-23 13:24:40 latitude: 53.5441 longitude: -2.7416 elevation: 124 2015-11-23 13:24:49 latitude: 53.5441 longitude: -2.7416 elevation: 122 2015-11-23 13:24:59 latitude: 53.5441 longitude: -2.7416 elevation: 120 2015-11-23 13:25:09 latitude: 53.5441 longitude: -2.7417 elevation: 120 2015-11-23 13:25:19 latitude: 53.5441 longitude: -2.7417 elevation: 121 2015-11-23 13:25:29 latitude: 53.5441 longitude: -2.7417 elevation: 120 2015-11-23 13:25:39 latitude: 53.5441 longitude: -2.7417 elevation: 120
Looping the Loop with SPL Iterators Array Functions – Filter Of course, we could always use a CallBackFilterIterator
Looping the Loop with SPL Iterators Array Functions – Map function map(Callable $callback, iterable $iterator) { foreach ($iterator as $key => $value) { yield $key => $callback($value); } }
Looping the Loop with SPL Iterators Array Functions – Map $distanceCalculator = new GpxReaderHelpersDistanceCalculator(); $mappedTrackingData = map( [$distanceCalculator, 'setDistanceProperty'], $gpxReader->getElements('trkpt') ); foreach ($mappedTrackingData as $time => $element) { ... }
Looping the Loop with SPL Iterators Array Functions – Map 2015-11-23 14:57:07 latitude: 53.5437 longitude: -2.7424 elevation: 103 distance from previous point: 6.93 m 2015-11-23 14:57:17 latitude: 53.5437 longitude: -2.7424 elevation: 100 distance from previous point: 1.78 m 2015-11-23 14:57:27 latitude: 53.5438 longitude: -2.7425 elevation: 89 distance from previous point: 11.21 m 2015-11-23 14:57:37 latitude: 53.5439 longitude: -2.7424 elevation: 83 distance from previous point: 9.23 m 2015-11-23 14:57:47 latitude: 53.5439 longitude: -2.7425 elevation: 92 distance from previous point: 5.40 m
Looping the Loop with SPL Iterators Array Functions – Walk iterator_apply() iterator_apply( Traversable $iterator, Callable $callback [, array $args = NULL ] ) : int
Looping the Loop with SPL Iterators Array Functions – Reduce function reduce(iterable $iterator, Callable $callback, $initial = null) { $result = $initial; foreach($iterator as $value) { $result = $callback($result, $value); } return $result; }
Looping the Loop with SPL Iterators Array Functions – Reduce $distanceCalculator = new GpxReaderHelpersDistanceCalculator(); $totalDistance = reduce( map( [$distanceCalculator, 'setDistanceProperty'], $gpxReader->getElements('trkpt') ), function($runningTotal, $value) { return $runningTotal + $value->distance; }, 0.0 );
Looping the Loop with SPL Iterators Array Functions – Reduce Total distance travelled is 4.33 km
Looping the Loop with SPL Iterators Array Functions – Other Iterator Functions Iterator_count() iterator_count ( Traversable $iterator ) : int
Looping the Loop with SPL Iterators Array Functions – Other Iterator Functions Iterator_to_array() iterator_to_array ( Traversable $iterator [, bool $use_keys = TRUE ] ) : array
Looping the Loop with SPL Iterators
Looping the Loop with SPL Iterators A Functional Guide to Cat Herding with PHP Generators • https://markbakeruk.net/2016/01/19/a-functional-guide-to-cat-herding-with-php-generators/ • https://markbakeruk.net/2020/01/05/filtering-and-mapping-with-spl-iterators/ • https://markbakeruk.net/2019/12/31/parallel-looping-in-php-with-spls-multipleiterator/
Looping the Loop with SPL Iterators Iterating PHP Iterators By Cal Evans https://leanpub.com/iteratingphpiterators by Joshua Thijssen https://www.phparch.com/books/mastering-the-spl-library/
Who am I? Mark Baker Most Recently: Senior Software Engineer MessageBird BV, Amsterdam Coordinator and Developer of: Open Source PHPOffice library PHPExcel, PHPWord, PHPPowerPoint, PHPProject, PHPVisio Minor contributor to PHP core (SPL DataStructures) Other small open source libraries available on github @Mark_Baker https://github.com/MarkBaker http://uk.linkedin.com/pub/mark-baker/b/572/171 http://markbakeruk.net Looping the Loop with SPL Iterators

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Looping the Loop with SPL Iterators

  • 1.
  • 2.
    Looping the Loopwith SPL Iterators What is an Iterator? An Iterator is an object that enables a programmer to traverse a container, particularly lists. A Behavioural Design Pattern (GoF)
  • 3.
    Looping the Loopwith SPL Iterators What is an Iterator? $dataSet = ['A', 'B', 'C']; foreach($dataSet as $key => $value) { echo "{$key} => {$value}", PHP_EOL; }
  • 4.
    Looping the Loopwith SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
  • 5.
    Looping the Loopwith SPL Iterators What is an Iterator? $data = ['A', 'B', 'C']; $dataSet = new ArrayIterator($data); foreach($dataSet as $key => $value) { echo "{$key} => {$value}", PHP_EOL; }
  • 6.
    Looping the Loopwith SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
  • 7.
    Looping the Loopwith SPL Iterators What is an Iterator? interface Iterator extends Traversable { /* Methods */ abstract public current ( void ) : mixed abstract public key ( void ) : scalar abstract public next ( void ) : void abstract public rewind ( void ) : void abstract public valid ( void ) : bool }
  • 8.
    Looping the Loopwith SPL Iterators What is an Iterator? $data = ['A', 'B', 'C']; $iterator = new ArrayIterator($data); $iterator->rewind(); while ($iterator->valid()) { $key = $iterator->key(); $value = $iterator->current(); echo "{$key} => {$value}", PHP_EOL; $iterator->next(); }
  • 9.
    Looping the Loopwith SPL Iterators What is an Iterator? 0 => A 1 => B 2 => C
  • 10.
    Looping the Loopwith SPL Iterators
  • 11.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate
  • 12.
    Looping the Loopwith SPL Iterators The Iterable Tree Not all iterables are equal You can count the elements in an array ! Can you count the elements in an Iterator?
  • 13.
    Looping the Loopwith SPL Iterators The Iterable Tree Not all iterables are equal You can access the elements of an array by their index ! Can you access the elements of an Iterator by index ?
  • 14.
    Looping the Loopwith SPL Iterators The Iterable Tree Not all iterables are equal You can rewind an Iterator ! Can you rewind a Generator ?
  • 15.
    Looping the Loopwith SPL Iterators The Iterable Tree Not all iterables are equal Iterator_* functions (e.g. iterator_to_array) work on Iterators ? Can you use iterator_* functions on an IteratorAggregate ?
  • 16.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Iterable is a pseudo-type introduced in PHP 7.1. It accepts any array, or any object that implements the Traversable interface. Both of these types are iterable using foreach.
  • 17.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate An array in PHP is an ordered map, a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and more. The foreach control structure exists specifically for arrays.
  • 18.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Abstract base interface to detect if a class is traversable using foreach. It cannot be implemented alone in Userland code; but instead must be implemented through either IteratorAggregate or Iterator. Internal (built-in) classes that implement this interface can be used in a foreach construct and do not need to implement IteratorAggregate or Iterator.
  • 19.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Abstract base interface to detect if a class is traversable using foreach. It cannot be implemented alone in Userland code; but instead must be implemented through either IteratorAggregate or Iterator. PDOStatement DatePeriod SimpleXMLElement
  • 20.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate An Interface for external iterators or objects that can be iterated themselves internally. PHP already provides a number of iterators for many day to day tasks within the Standard PHP Library (SPL). SPL Iterators SPL DataStructures WeakMaps (PHP 8)
  • 21.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate Generators provide an easy way to implement simple user-defined iterators without the overhead or complexity of implementing a class that implements the Iterator interface. This flexibility does come at a cost, however: generators are forward-only iterators, and cannot be rewound once iteration has started.
  • 22.
    Looping the Loopwith SPL Iterators The Iterable Tree iterable array Traversable Iterator Generator IteratorAggregate IteratorAggregate is a special interface for implementing an abstraction layer between user code and iterators. Implementing an IteratorAggregate will allow you to delegate the work of iteration to a separate class, while still enabling you to use the collection inside a foreach loop.
  • 23.
    Looping the Loopwith SPL Iterators
  • 24.
    Looping the Loopwith SPL Iterators Implementing an Iterator interface Iterator extends Traversable { /* Methods */ abstract public current ( void ) : mixed abstract public key ( void ) : scalar abstract public next ( void ) : void abstract public rewind ( void ) : void abstract public valid ( void ) : bool }
  • 25.
    Looping the Loopwith SPL Iterators Implementing an Iterator class Utf8StringIterator implements Iterator { private $string; private $offset = 0; private $length = 0; public function __construct(string $string) { $this->string = $string; $this->length = iconv_strlen($string); } public function valid(): bool { return $this->offset < $this->length; } ... }
  • 26.
    Looping the Loopwith SPL Iterators Implementing an Iterator class Utf8StringIterator implements Iterator { ... public function rewind(): void { $this->offset = 0; } public function current(): string { return iconv_substr($this->string, $this->offset, 1); } public function key(): int { return $this->offset; } public function next(): void { ++$this->offset; } }
  • 27.
    Looping the Loopwith SPL Iterators Implementing an Iterator $stringIterator = new Utf8StringIterator('Καλησπέρα σε όλους'); foreach($stringIterator as $character) { echo "[{$character}]"; }
  • 28.
    Looping the Loopwith SPL Iterators Implementing an Iterator [Κ][α][λ][η][σ][π][έ][ρ][α][ ][σ][ε][ ][ό][λ][ο][υ][ς]
  • 29.
    Looping the Loopwith SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { private $fileHandle; private $line = 1; public function __construct(string $fileName) { $this->fileHandle = fopen($fileName, 'r'); } public function __destruct() { fclose($this->fileHandle); } }
  • 30.
    Looping the Loopwith SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { ... public function current(): string { $fileData = fgets($this->fileHandle); return rtrim($fileData, "n"); } public function key(): int { return $this->line; } public function next(): void { ++$this->line; } }
  • 31.
    Looping the Loopwith SPL Iterators Implementing an Iterator class FileLineIterator implements Iterator { ... public function rewind(): void { fseek($this->fileHandle, 0); $this->line = 1; } public function valid(): bool { return !feof($this->fileHandle); } }
  • 32.
    Looping the Loopwith SPL Iterators Implementing an Iterator $fileLineIterator = new FileLineIterator(__FILE__); foreach($fileLineIterator as $lineNumber => $fileLine) { echo "{$lineNumber}: {$fileLine}", PHP_EOL; }
  • 33.
    Looping the Loopwith SPL Iterators Implementing an Iterator 1: <?php 2: 3: class FileLineIterator implements Iterator { 4: private $fileHandle; 5: private $line = 1; 6: 7: public function __construct(string $fileName) { 8: $this->fileHandle = fopen($fileName, 'r’); 9: } 10: …
  • 34.
    Looping the Loopwith SPL Iterators
  • 35.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): array { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return array_map(fn(array $user): User => User::fromArray($user), $users); } }
  • 36.
    Looping the Loopwith SPL Iterators class UserRepository { // ... /** * @return User[] */ public function all(): array { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return array_map(fn(array $user): User => User::fromArray($user), $users); } }
  • 37.
    Looping the Loopwith SPL Iterators class UserCollection extends ArrayIterator { }
  • 38.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection( array_map(fn(array $user): User => User::fromArray($user), $users) ); } }
  • 39.
    Looping the Loopwith SPL Iterators class UserCollection extends ArrayIterator { public function current(): User { return User::fromArray(parent::current()); } }
  • 40.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection($users); } }
  • 41.
    Looping the Loopwith SPL Iterators
  • 42.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator)
  • 43.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable
  • 44.
    Looping the Loopwith SPL Iterators ArrayIterator – Countable interface Countable { /* Methods */ abstract public count ( void ) : int }
  • 45.
    Looping the Loopwith SPL Iterators ArrayIterator – Countable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userCount = count($userList); echo "There are {$userCount} users in this list", PHP_EOL;
  • 46.
    Looping the Loopwith SPL Iterators ArrayIterator – Countable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); echo "There are {$userList->count()} users in this list", PHP_EOL;
  • 47.
    Looping the Loopwith SPL Iterators ArrayIterator – Countable There are 4 users in this list
  • 48.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable ArrayAccess
  • 49.
    Looping the Loopwith SPL Iterators ArrayIterator – ArrayAccess interface ArrayAccess { /* Methods */ abstract public offsetExists ( mixed $offset ) : bool abstract public offsetGet ( mixed $offset ) : mixed abstract public offsetSet ( mixed $offset , mixed $value ) : void abstract public offsetUnset ( mixed $offset ) : void }
  • 50.
    Looping the Loopwith SPL Iterators ArrayIterator – ArrayAccess $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); echo "The 3rd entry in the list is {$userList[2]}", PHP_EOL;
  • 51.
    Looping the Loopwith SPL Iterators ArrayIterator – ArrayAccess The 3rd entry in the list is user3
  • 52.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable
  • 53.
    Looping the Loopwith SPL Iterators ArrayIterator – Serializable interface Serializable { /* Methods */ abstract public serialize ( void ) : string abstract public unserialize ( string $serialized ) : void }
  • 54.
    Looping the Loopwith SPL Iterators ArrayIterator – Serializable $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); var_dump(serialize($userList));
  • 55.
    Looping the Loopwith SPL Iterators ArrayIterator – Serializable string(117) "O:8:"UserList":4:{i:0;i:0;i:1;a:4:{i:0;s:5:"user1"; i:1;s:5:"user2";i:2;s:5:"user3";i:3;s:5:"user4";}i:2; a:0:{}i:3;N;}"
  • 56.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator)
  • 57.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator SeekableIterator extends Iterator { /* Methods */ abstract public seek ( int $position ) : void /* Inherited methods */ abstract public Iterator::current ( void ) : mixed abstract public Iterator::key ( void ) : scalar abstract public Iterator::next ( void ) : void abstract public Iterator::rewind ( void ) : void abstract public Iterator::valid ( void ) : bool }
  • 58.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userList->seek(2); while ($userList->valid()) { echo $userList->current(), PHP_EOL; $userList->next(); }
  • 59.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator user3 user4
  • 60.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new UserList($userData); $userList->seek(2); foreach($userList as $userName) { echo $userName, PHP_EOL; }
  • 61.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator user1 user2 user3 user4 
  • 62.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator $userData = ['A' => 'user1', 'B' => 'user2', 'C' => 'user3', 'D' => 'user4']; $userList = new UserList($userData); $userList->seek('C'); while ($userList->valid()) { echo $userList->current(), PHP_EOL; $userList->next(); }
  • 63.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator PHP7 Warning: ArrayIterator::seek() expects parameter 1 to be int, string given 
  • 64.
    Looping the Loopwith SPL Iterators ArrayIterator – SeekableIterator PHP8 Fatal error: Uncaught TypeError ArrayIterator::seek(): Argument #1 ($position) must be of type int, string given 
  • 65.
    Looping the Loopwith SPL Iterators ArrayIterator Implements: Countable ArrayAccess Serializable SeekableIterator (which entends Iterator) Also provides methods for sorting Doesn’t work with array_* functions
  • 66.
    Looping the Loopwith SPL Iterators
  • 67.
    Looping the Loopwith SPL Iterators
  • 68.
    Looping the Loopwith SPL Iterators LimitIterator $userData = ['user1', 'user2', 'user3', 'user4']; $userList = new LimitIterator( new UserList($userData), 2, 1 ); foreach($userList as $value) { echo $value, PHP_EOL; }
  • 69.
    Looping the Loopwith SPL Iterators LimitIterator user3
  • 70.
    Looping the Loopwith SPL Iterators InfiniteIterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-08'))->format('w'); $weekdayList = new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ); foreach($weekdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
  • 71.
    Looping the Loopwith SPL Iterators InfiniteIterator Tues Wed Thurs Fri Sat Sun Mon Tues Wed Thurs Fri Sat Sun Mon
  • 72.
    Looping the Loopwith SPL Iterators CallbackFilterIterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-15'))->format('w'); $workdayList = new CallbackFilterIterator( new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ), fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
  • 73.
    Looping the Loopwith SPL Iterators CallbackFilterIterator Tues Wed Thurs Fri Mon Tues Wed Thurs Fri Mon
  • 74.
    Looping the Loopwith SPL Iterators
  • 75.
    Looping the Loopwith SPL Iterators FilterIterator abstract FilterIterator extends IteratorIterator implements OuterIterator { /* Methods */ public abstract accept ( void ) : bool public __construct ( Iterator $iterator ) public current ( void ) : mixed public getInnerIterator ( void ) : Iterator public key ( void ) : mixed public next ( void ) : void public rewind ( void ) : void public valid ( void ) : bool }
  • 76.
    Looping the Loopwith SPL Iterators FilterIterator class ImageFileIterator extends FilterIterator { // Overwrite the constructor to automagically create an inner iterator // to iterate the file system when given a path name. public function __construct(string $path) { parent::__construct(new FilesystemIterator($path)); } // Overwrite the accept method to perform a super simple test to // determine if the files found were images or not. public function accept(): bool { $fileObject = $this->getInnerIterator()->current(); return preg_match('/^(?:gif|jpe?g|png)$/i', $fileObject->getExtension()); } }
  • 77.
    Looping the Loopwith SPL Iterators FilterIterator class ImageFileIterator extends FilterIterator { // Overwrite the constructor to automagically create an inner iterator // to iterate the file system when given a path name. public function __construct(string $path) { parent::__construct(new FilesystemIterator($path)); } // Overwrite the accept method to perform a super simple test to // determine if the files found were images or not. public function accept(): bool { return preg_match('/^(?:gif|jpe?g|png)$/i', $this->getExtension()); } }
  • 78.
    Looping the Loopwith SPL Iterators FilterIterator $path = dirname(__FILE__); foreach(new ImageFileIterator($path) as $imageObject) { echo $imageObject->getBaseName(), PHP_EOL; }
  • 79.
    Looping the Loopwith SPL Iterators FilterIterator anubis.jpg Carpet.jpg Crazy Newspaper Headlines.jpg elephpant.jpg Pie Chart.jpg PowerOfBooks.jpg Struggling-Team.png TeddyBears.jpg
  • 80.
    Looping the Loopwith SPL Iterators Iterator Keys class ImageFileIterator extends FilterIterator { ... // Overwrite the key method to return the file extension as the key public function key(): string { return $this->getExtension(); } } foreach(new ImageFileIterator($path) as $extension => $imageObject) { echo "{$extension} => {$imageObject->getBaseName()}", PHP_EOL; }
  • 81.
    Looping the Loopwith SPL Iterators Iterator Keys jpg => anubis.jpg jpg => Carpet.jpg jpg => Crazy Newspaper Headlines.jpg jpg => elephpant.jpg jpg => Pie Chart.jpg jpg => PowerOfBooks.jpg png => Struggling-Team.png jpg => TeddyBears.jpg
  • 82.
    Looping the Loopwith SPL Iterators Iterator Keys class ImageFileIterator extends FilterIterator { ... // Overwrite the key method to return the last modified date/time as the key public function key(): DateTime { return DateTime::createFromFormat('U', $this->getMTime()); } } foreach(new ImageFileIterator($path) as $date => $imageObject) { echo "{$date->format('Y-m-d H:i:s')} => {$imageObject->getBaseName()}", PHP_EOL; }
  • 83.
    Looping the Loopwith SPL Iterators Iterator Keys 2012-03-24 00:38:24 => anubis.jpg 2013-01-27 22:32:20 => Carpet.jpg 2013-03-07 12:16:24 => Crazy Newspaper Headlines.jpg 2012-02-16 22:31:56 => elephpant.jpg 2012-10-09 11:51:56 => Pie Chart.jpg 2012-07-17 12:22:32 => PowerOfBooks.jpg 2012-12-30 18:14:24 => Struggling-Team.png 2012-01-31 11:17:32 => TeddyBears.jpg
  • 84.
    Looping the Loopwith SPL Iterators
  • 85.
    Looping the Loopwith SPL Iterators MultipleIterator $dates = ['Q1-2019', 'Q2-2019', 'Q3-2019', 'Q4-2019']; $budget = [1200, 1300, 1400, 1500]; $expenditure = [1250, 1315, 1440, 1485]; $budgetElements = count($budget); for ($i = 0; $i < $budgetElements; $i++) { echo "{$dates[$i]} - {$budget[$i]}, {$expenditure[$i]}", PHP_EOL; }
  • 86.
    Looping the Loopwith SPL Iterators MultipleIterator $dates = ['Q1-2019', 'Q2-2019', 'Q3-2019', 'Q4-2019']; $budget = [1200, 1300, 1400, 1500]; $expenditure = [1250, 1315, 1440, 1485]; foreach($dates as $key => $period) { echo "{$period} - {$budget[$key]}, {$expenditure[$key]}", PHP_EOL; }
  • 87.
    Looping the Loopwith SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
  • 88.
    Looping the Loopwith SPL Iterators MultipleIterator function wrapArrayAsIterator(array $array) { return new ArrayIterator($array); } $combinedIterable = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $combinedIterable->attachIterator(wrapArrayAsIterator($dates), 'date'); $combinedIterable->attachIterator(wrapArrayAsIterator($budget), 'budget'); $combinedIterable->attachIterator(wrapArrayAsIterator($expenditure), 'expenditure');
  • 89.
    Looping the Loopwith SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { echo $dateValues['date'], " - {$dateValues['budget']}, {$dateValues['expenditure']}", PHP_EOL; }
  • 90.
    Looping the Loopwith SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { [$date, $budget, $expenditure] = $dateValues; echo "{$date} - {$budget}, {$expenditure}", PHP_EOL; }
  • 91.
    Looping the Loopwith SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
  • 92.
    Looping the Loopwith SPL Iterators MultipleIterator function wrapArrayAsIterator(array $array) { return new ArrayIterator($array); } $combinedIterable = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $combinedIterable->attachIterator(wrapArrayAsIterator($dates), 'date'); $combinedIterable->attachIterator(wrapArrayAsIterator($budget), 'budget'); $combinedIterable->attachIterator(wrapArrayAsIterator($expenditure), 'expenditure');
  • 93.
    Looping the Loopwith SPL Iterators MultipleIterator foreach($combinedIterable as $dateValues) { extract($dateValues); echo "{$date} - {$budget}, {$expenditure}", PHP_EOL; }
  • 94.
    Looping the Loopwith SPL Iterators MultipleIterator Q1-2019 - 1200, 1250 Q2-2019 - 1300, 1315 Q3-2019 - 1400, 1440 Q4-2019 - 1500, 1485
  • 95.
    Looping the Loopwith SPL Iterators MultipleIterator $allocations = $totalAdvance->allocateTo(count($cars)); foreach ($cars as $i => $car) { $car->setAdvance($allocations[$i]); }
  • 96.
    Looping the Loopwith SPL Iterators MultipleIterator $allocations = $totalAdvance->allocateTo(count($cars)); $advanceAllocations = new MultipleIterator(MultipleIterator::MIT_KEYS_ASSOC); $advanceAllocations->attachIterator(ArrayIterator($cars), 'car'); $advanceAllocations->attachIterator(ArrayIterator($allocations), 'advance'); foreach($advanceAllocations as $advanceAllocation) { extract($advanceAllocation); $car->setAdvance($advance); }
  • 97.
    Looping the Loopwith SPL Iterators
  • 98.
    Looping the Loopwith SPL Iterators Inner and Outer Iterators Inner Iterator Implements Iterator, or extends a class that implements Iterator ArrayIterator SeekableIterator FilesystemIterator MultipleIterator
  • 99.
    Looping the Loopwith SPL Iterators Inner and Outer Iterators Outer Iterator Implements OuterIterator, or extends an Iterator that already implements OuterIterator LimitIterator InfiniteIterator FilterIterator CallbackFilterIterator
  • 100.
    Looping the Loopwith SPL Iterators Recursive Iterators A RecursiveIterator defines methods to allow iteration over hierarchical data structures. Nested Arrays (and Objects if using ArrayAccess) Filesystem Directories/Folders
  • 101.
    Looping the Loopwith SPL Iterators
  • 102.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); $users = $statement->fetchAll(); return new UserCollection( array_map(fn(array $user): User => User::fromArray($user), $users) ); } }
  • 103.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): Generator { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); while ($user = $statement->fetch()) { yield User::fromArray($user); } } }
  • 104.
    Looping the Loopwith SPL Iterators class UserRepository { // ... /** * @return Generator|User[] */ public function all(): Generator { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); $statement->execute(); while ($user = $statement->fetch()) { yield User::fromArray($user); } } }
  • 105.
    Looping the Loopwith SPL Iterators IteratorAggregate IteratorAggregate extends Traversable { /* Methods */ abstract public getIterator ( void ) : Traversable }
  • 106.
    Looping the Loopwith SPL Iterators class UserCollection implements IteratorAggregate { private PDOStatement $pdoStatement; public function __construct(PDOStatement $pdoStatement) { $this->pdoStatement = $pdoStatement; } public function getIterator(): Traversable { $this->pdoStatement->execute(); while ($user = $this->pdoStatement->fetch()) { yield User::fromArray($user); } } }
  • 107.
    Looping the Loopwith SPL Iterators class UserRepository { // ... public function all(): UserCollection { $userQuery = 'SELECT * FROM `users` ...'; $statement = $this->pdo->prepare($userQuery); return new UserCollection($statement); } }
  • 108.
    Looping the Loopwith SPL Iterators Implementing a Fluent Nested Iterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-09-15'))->format('w'); $workdayList = new CallbackFilterIterator( new LimitIterator( new InfiniteIterator( new ArrayIterator($weekdayNames) ), $todayOffset, 14 ), fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
  • 109.
    Looping the Loopwith SPL Iterators Implementing a Fluent Nested Iterator class FluentNestedIterator implements IteratorAggregate { protected iterable $iterator; public function __construct(iterable $iterator) { $this->iterator = $iterator; } public function with(string $iterable, ...$args): self { $this->iterator = new $iterable($this->iterator, ...$args); return $this; } public function getIterator() { return $this->iterator; } }
  • 110.
    Looping the Loopwith SPL Iterators Implementing a Fluent Nested Iterator $weekdayNames = ['Sun', 'Mon', 'Tues', 'Wed', 'Thurs', 'Fri', 'Sat']; $todayOffset = (int) (new DateTime('2020-10-08'))->format('w'); $workdayList = (new FluentNestedIterator(new ArrayIterator($weekdayNames))) ->with(InfiniteIterator::class) ->with(LimitIterator::class, $todayOffset, 14) ->with( CallbackFilterIterator::class, fn($dayName): bool => $dayName !== 'Sat' && $dayName !== 'Sun' ); foreach($workdayList as $dayOfWeek) { echo $dayOfWeek, PHP_EOL; }
  • 111.
    Looping the Loopwith SPL Iterators Implementing a Fluent Nested Iterator Thurs Fri Mon Tues Wed Thurs Fri Mon Tues Wed
  • 112.
    Looping the Loopwith SPL Iterators
  • 113.
    Looping the Loopwith SPL Iterators Array Functions Don’t work with Traversables
  • 114.
    Looping the Loopwith SPL Iterators Array Functions Don’t work with Traversables
  • 115.
    Looping the Loopwith SPL Iterators Array Functions – Filter function filter(iterable $iterator, Callable $callback = null) { if ($callback === null) { $callback = 'iterableFilterNotEmpty'; } foreach ($iterator as $key => $value) { if ($callback($value)) { yield $key => $value; } } }
  • 116.
    Looping the Loopwith SPL Iterators Array Functions – Filter $startTime = new DateTime('2015-11-23 13:20:00Z'); $endTime = new DateTime('2015-11-23 13:30:00Z'); $timeFilter = function($timestamp) use ($startTime, $endTime) { return $timestamp >= $startTime && $timestamp <= $endTime; }; $filteredTrackingData = filter( $gpxReader->getElements('trkpt'), $timeFilter, ARRAY_FILTER_USE_KEY ); foreach ($filteredTrackingData as $time => $element) { ... }
  • 117.
    Looping the Loopwith SPL Iterators Array Functions – Filter 2015-11-23 13:24:40 latitude: 53.5441 longitude: -2.7416 elevation: 124 2015-11-23 13:24:49 latitude: 53.5441 longitude: -2.7416 elevation: 122 2015-11-23 13:24:59 latitude: 53.5441 longitude: -2.7416 elevation: 120 2015-11-23 13:25:09 latitude: 53.5441 longitude: -2.7417 elevation: 120 2015-11-23 13:25:19 latitude: 53.5441 longitude: -2.7417 elevation: 121 2015-11-23 13:25:29 latitude: 53.5441 longitude: -2.7417 elevation: 120 2015-11-23 13:25:39 latitude: 53.5441 longitude: -2.7417 elevation: 120
  • 118.
    Looping the Loopwith SPL Iterators Array Functions – Filter Of course, we could always use a CallBackFilterIterator
  • 119.
    Looping the Loopwith SPL Iterators Array Functions – Map function map(Callable $callback, iterable $iterator) { foreach ($iterator as $key => $value) { yield $key => $callback($value); } }
  • 120.
    Looping the Loopwith SPL Iterators Array Functions – Map $distanceCalculator = new GpxReaderHelpersDistanceCalculator(); $mappedTrackingData = map( [$distanceCalculator, 'setDistanceProperty'], $gpxReader->getElements('trkpt') ); foreach ($mappedTrackingData as $time => $element) { ... }
  • 121.
    Looping the Loopwith SPL Iterators Array Functions – Map 2015-11-23 14:57:07 latitude: 53.5437 longitude: -2.7424 elevation: 103 distance from previous point: 6.93 m 2015-11-23 14:57:17 latitude: 53.5437 longitude: -2.7424 elevation: 100 distance from previous point: 1.78 m 2015-11-23 14:57:27 latitude: 53.5438 longitude: -2.7425 elevation: 89 distance from previous point: 11.21 m 2015-11-23 14:57:37 latitude: 53.5439 longitude: -2.7424 elevation: 83 distance from previous point: 9.23 m 2015-11-23 14:57:47 latitude: 53.5439 longitude: -2.7425 elevation: 92 distance from previous point: 5.40 m
  • 122.
    Looping the Loopwith SPL Iterators Array Functions – Walk iterator_apply() iterator_apply( Traversable $iterator, Callable $callback [, array $args = NULL ] ) : int
  • 123.
    Looping the Loopwith SPL Iterators Array Functions – Reduce function reduce(iterable $iterator, Callable $callback, $initial = null) { $result = $initial; foreach($iterator as $value) { $result = $callback($result, $value); } return $result; }
  • 124.
    Looping the Loopwith SPL Iterators Array Functions – Reduce $distanceCalculator = new GpxReaderHelpersDistanceCalculator(); $totalDistance = reduce( map( [$distanceCalculator, 'setDistanceProperty'], $gpxReader->getElements('trkpt') ), function($runningTotal, $value) { return $runningTotal + $value->distance; }, 0.0 );
  • 125.
    Looping the Loopwith SPL Iterators Array Functions – Reduce Total distance travelled is 4.33 km
  • 126.
    Looping the Loopwith SPL Iterators Array Functions – Other Iterator Functions Iterator_count() iterator_count ( Traversable $iterator ) : int
  • 127.
    Looping the Loopwith SPL Iterators Array Functions – Other Iterator Functions Iterator_to_array() iterator_to_array ( Traversable $iterator [, bool $use_keys = TRUE ] ) : array
  • 128.
    Looping the Loopwith SPL Iterators
  • 129.
    Looping the Loopwith SPL Iterators A Functional Guide to Cat Herding with PHP Generators • https://markbakeruk.net/2016/01/19/a-functional-guide-to-cat-herding-with-php-generators/ • https://markbakeruk.net/2020/01/05/filtering-and-mapping-with-spl-iterators/ • https://markbakeruk.net/2019/12/31/parallel-looping-in-php-with-spls-multipleiterator/
  • 130.
    Looping the Loopwith SPL Iterators Iterating PHP Iterators By Cal Evans https://leanpub.com/iteratingphpiterators by Joshua Thijssen https://www.phparch.com/books/mastering-the-spl-library/
  • 131.
    Who am I? MarkBaker Most Recently: Senior Software Engineer MessageBird BV, Amsterdam Coordinator and Developer of: Open Source PHPOffice library PHPExcel, PHPWord, PHPPowerPoint, PHPProject, PHPVisio Minor contributor to PHP core (SPL DataStructures) Other small open source libraries available on github @Mark_Baker https://github.com/MarkBaker http://uk.linkedin.com/pub/mark-baker/b/572/171 http://markbakeruk.net Looping the Loop with SPL Iterators