Turn on the Generator!

Zombie apocalypses are the worst. Low on food, low on water, low on power. The worst part about zombie apocalypses are the waiting. But we can prepare for that…

This is a talk about the new yield keyword. How it works, what it’s good for, and how to make the most of it. We’ll unpack the structure of a generator, and replace some old parts of our application with new, efficient and wonderfully readable code.

Join me as we fight off the hungry hordes, and unlock the true power hidden in PHP generators.

Transcript

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4. TURN ON
   THE GENERATOR
   

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5. ARRAYS
   $coordinates = [
   [039.842286, -108.457031],
   [032.916485, -113.906250],
   [033.431441, -099.404297],
   [042.032974, -097.031250],
   [050.064192, -106.962891],
   ];
   foreach ($coordinates as $coordinate) {
   CDC::innoculate($coordinate);
   }
   print "innoculate " . count($coordinates) . " places";
   $filter = function($coordinate) {
   return $coordinate[1] < -98;
   };
   $breakouts = array_filter($coordinates, $filter);
   

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6. THINGS LIKE ARRAYS
   $secret = new DomDocument();
   $secret->loadHTMLFile(
   "secure/2021/lockdown-protocols.html"
   );
   $steps = $secret->getElementsByTagName("h1");
   foreach ($steps as $step) {
   Military::follow($step);
   }
   print "followed " . $steps->length . " steps";
   

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7. THINGS LIKE ARRAYS
   is_array($coordinates) // 㱺 true
   is_array($steps) // 㱺 false
   $coordinates instanceof Traversable // 㱺 error
   $steps instanceof Traversable // 㱺 true
   

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8. THINGS LIKE ARRAYS
   class ContainmentProtocols
   implements Traversable {
   } // 㱺 error
   

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9. ITERATORS
   class EvacuationProcedures
   implements Iterator {
   function current();
   function key();
   function next();
   function rewind();
   function valid();
   }
   

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10. ITERATORS
    class EvacuationProcedures
    implements Iterator {
    /**
    * Returns the current value
    * where the array is at
    */
    function current();
    function key();
    function next();
    function rewind();
    function valid();
    }
    

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11. ITERATORS
    class EvacuationProcedures
    implements Iterator {
    function current();
    /**
    * Returns the pointer to
    * the current position
    */
    function key();
    function next();
    function rewind();
    function valid();
    }
    

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12. ITERATORS
    class EvacuationProcedures
    implements Iterator {
    function current();
    function key();
    /**
    * Advances the pointer to
    * the next position
    */
    function next();
    function rewind();
    function valid();
    }
    

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13. ITERATORS
    class EvacuationProcedures
    implements Iterator {
    function current();
    function key();
    function next();
    /**
    * Moves the pointer back
    * to the beginning
    */
    function rewind();
    function valid();
    }
    

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14. ITERATORS
    class EvacuationProcedures
    implements Iterator {
    function current();
    function key();
    function next();
    function rewind();
    /**
    * Indicates whether there
    * are more values to go
    */
    function valid();
    }
    

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15. ABSTRACTION
    

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16. ABSTRACTION
    function numberForPatient($patient) {
    return Registry::getNewNumber($patient);
    }
    function admitPatients(array $patients) {
    $numbers = array_map(
    "numberForPatient", $patients
    );
    for ($i = 0; $i < count($patients); $i++) {
    Station::assignPatientToRoom(
    $numbers[$i], $patients[$i]
    );
    }
    }
    

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17. ABSTRACTION
    class Patients
    implements Iterator {
    // ...
    function key() {
    return $this->patients[
    $this->pointer
    ];
    }
    function current() {
    return numberForPatient(
    $this->key()
    );
    }
    }
    

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18. ABSTRACTION
    $intake = [
    "Cathy",
    "Cal",
    "Joe",
    ];
    $patients = new Patients($intake);
    foreach ($patients as $patient => $number) {
    Station::assignPatientToRoom(
    $number, $patient
    );
    }
    

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19. ABSTRACTION
    class ClassifiedPatients
    implements Iterator {
    // ...construct($patients)
    function key() {
    return md5(
    $this->patients->key()
    );
    }
    }
    

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20. ABSTRACTION
    $intake = [
    "Cathy",
    "Cal",
    "Joe",
    ];
    $patients = new ClassifiedPatients(
    new Patients($intake)
    );
    foreach ($patients as $patient => $number) {
    Station::assignPatientToRoom(
    $number, $patient
    );
    }
    

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21. ABSTRACTION
    class SearchablePatients
    implements IteratorAggregate {
    // ...construct($patients)
    function getIterator() {
    return $this->patients;
    }
    function searchFor($patient) {
    $i = 0;
    for ($this->patients as $next => $number) {
    if ($patient == $next) {
    return $i;
    }
    $i++;
    }
    }
    }
    

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22. ABSTRACTION
    class CountablePatients
    implements IteratorAggregate, Countable {
    // ...construct($patients)
    function count() {
    return iterator_count($this->patients);
    }
    }
    $countable = new CountablePatients(
    new Patients($intake)
    );
    count($countable); // 㱺 3
    

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23. ABSTRACTION
    class SeekablePatients
    implements IteratorAggregate, SeekableIterator {
    // ...construct($patients)
    function seek($position) {
    $i = 0;
    foreach ($this->patients as $patient) {
    if ($i++ == $position) {
    return;
    }
    }
    }
    }
    $seekable = new SeekablePatients(
    new Patients($intake)
    );
    $seekable
    ->seek(1)
    ->current(); // 㱺 "Cal"
    

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24. ABSTRACTION
    class ArrayablePatients
    implements IteratorAggregate, ArrayAccess {
    // ...construct($patients)
    function offsetExists($offset);
    function offsetGet($offset);
    function offsetSet($offset, $value);
    function offsetUnset($offset);
    }
    $array = new ArrayablePatients(
    new Patients($intake)
    );
    $array[1]; // 㱺 "Cal"
    

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25. ABSTRACTION
    • AppendIterator
    • ArrayIterator
    • CachingIterator
    • CallbackFilterIterator
    • DirectoryIterator
    • EmptyIterator
    • FilesystemIterator
    • FilterIterator
    • GlobIterator
    

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26. ABSTRACTION
    • InfiniteIterator
    • IteratorIterator
    • LimitIterator
    • Mul0pleIterator
    • NoRewindIterator
    • ParentIterator
    • RecursiveArrayIterator
    • RecursiveCachingIterator
    • RecursiveCallbackFilterIterator
    

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27. ABSTRACTION
    • RecursiveDirectoryIterator
    • RecursiveFilterIterator
    • RecursiveIteratorIterator
    • RecursiveRegexIterator
    • RecursiveTreeIterator
    • RegexIterator
    

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28. PROBLEMS
    $patients = new Patients($intake);
    array_filter($patients, function($number) {
    // 㱺 error
    });
    

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29. PROBLEMS
    // github.com/nikic/iter
    $patients = new Patients($intake);
    iter\filter(function($number) {
    // 㱺 ok
    }, $patients);
    

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30. PROBLEMS
    // github.com/nikic/iter
    $patients = new Patients($intake);
    iter\filter(function($number) {
    // 㱺 ok
    }, $patients);
    

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33. ABSTRACTION
    

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34. ABSTRACTION
    $instructions = "";
    $chapters = file_get_contents(
    "delta/operating-manual.txt"
    );
    foreach ($chapters as $chapter) {
    $instructions .= file_get_contents(
    "delta/operating-manual/" . $chapter
    );
    }
    print "instructions: \n\n" . $instructions;
    print "you've escaped!";
    

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35. ABSTRACTION
    class OperatingManual
    implements Iterator {
    private $chapters;
    function __construct($file) {
    $this->chapters = file_get_contents(
    $file
    );
    }
    }
    

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36. ABSTRACTION
    class OperatingManual
    implements Iterator {
    // ...
    private $chapter = 0;
    function rewind() {
    $this->chapter = 0;
    }
    function next() {
    $this->chapter++;
    }
    }
    

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37. ABSTRACTION
    class OperatingManual
    implements Iterator {
    // ...
    function key() {
    return $this->chapter[
    $this->chapter
    ];
    }
    function current() {
    return file_get_contents(
    $this->key()
    );
    }
    function valid() {
    isset(
    $this->chapters[
    $this->chapter
    ]
    );
    }
    }
    

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38. ABSTRACTION
    $manual = new OperatingManual(
    "delta/operating-manual.txt"
    );
    foreach ($manual as $chapter) {
    print "next chapter: \n\n" . $chapter;
    }
    print "you've escaped!";
    

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42. ABSTRACTION
    $manual = new OperatingManual(
    "delta/operating-manual.txt"
    );
    foreach ($manual as $chapter) {
    print "next chapter: \n\n" . $chapter;
    }
    print "you've escaped!";
    

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43. ITERATOR LIKE THINGS
    function OperatingManual($file) {
    $handle = fopen($file, "r");
    while (!feof($handle)) {
    yield file_get_contents(
    trim(fgets($handle))
    );
    }
    fclose($handle);
    }
    $manual = OperatingManual(
    "delta/operating-manual.txt"
    );
    

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44. ITERATOR LIKE THINGS
    print_r(get_class_methods($manual));
    // 㱺 Array
    // (
    // [0] => rewind
    // [1] => valid
    // [2] => current
    // [3] => key
    // [4] => next
    // [5] => send
    // [6] => throw
    // [7] => getReturn
    // [8] => __wakeup
    // )
    

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46. ARRAYS ARE
    LIKE ROLODEXES
    

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47. ASK FOR ITEM #3,
    AND YOU'LL GET ITEM #3
    

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48. IT'S PREDICTABLE
    

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49. FUNCTIONS ACT LIKE
    DATA TABLES
    

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50. PUT THE SAME
    THING IN...
    

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51. ...YOU GET THE
    SAME THING OUT
    

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52. IT'S PREDICTABLE
    

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53. NULL OBJECT PATTERN
    

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54. NULL OBJECT PATTERN
    function arrayToObject(array $data) {
    $encoded = json_encode($data);
    return json_decode($encoded);
    }
    $report = arrayToObject([
    "station" => [
    "armory" => [
    "safe" => [
    "weapons" => "one rifle",
    ],
    ],
    ],
    ]);
    

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55. NULL OBJECT PATTERN
    function searchForWeapons($report) {
    return $report
    ->station
    ->armory
    ->safe
    ->weapons;
    }
    print searchForWeapons(
    arrayToObject(["station" => null])
    );
    // 㱺 error: accessing $armory on null
    

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56. NULL OBJECT PATTERN
    function searchForWeapons($report) {
    if ($station = $report->station) {
    if ($armory = $station->armory) {
    // ...
    }
    }
    }
    

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57. NULL OBJECT PATTERN
    class Maybe {
    private $value;
    function __construct($value) {
    $this->value = $value;
    }
    function __get($property) {
    if (is_object($this->value)) {
    return new static(
    $this->value->$property
    );
    }
    }
    function value() {
    return $this->value;
    }
    }
    

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58. NULL OBJECT PATTERN
    function searchForWeapons($report) {
    return $report
    ->station
    ->armory
    ->safe
    ->weapons
    ->value();
    }
    print searchForWeapons(
    arrayToObject(["station" => null]);
    );
    // 㱺 null
    

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59. NULL OBJECT PATTERN
    static function from($value) {
    if ($value instanceof static) {
    return $value;
    }
    return new static($value);
    }
    static function generator($starting, $generator) {
    $monad = static::from($starting);
    $generator = $generator($monad);
    $next = $generator->current();
    while ($generator->valid()) {
    $monad = static::from($next);
    $next = $generator->send($monad);
    }
    return $generator->getReturn();
    }
    

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60. NULL OBJECT PATTERN
    $weapons = Maybe::generator(
    $report, function($report) {
    $station = yield $report->station;
    $armory = yield $station->armory;
    $safe = yield $armory->safe;
    return $safe->weapons;
    }
    );
    print $weapons;
    

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61. COROUTINES
    

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62. COROUTINES
    $people = [
    "Lorna",
    "Rob",
    "Chris",
    "Aaron",
    "Sara",
    ];
    $fences = [
    "next to the old car",
    "behind the kennel",
    "out back",
    ];
    

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63. COROUTINES
    function checkRations(array $people) {
    foreach ($people as $person) {
    print "checking rations for " . $person;
    yield showRationsFor($person);
    }
    }
    function watchFences(array $people, array $fences) {
    foreach ($fences as $fence) {
    $next = next($people);
    if ($next) {
    $next = reset($people);
    }
    print $next . " is watching " . $fence;
    yield watchFence($next, $fence);
    }
    }
    

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64. COROUTINES
    class Task {
    private $generator;
    function __construct($generator) {
    $this->generator = $generator;
    }
    function run() {
    $this->generator->next();
    }
    function valid() {
    return $this->generator->valid();
    }
    }
    

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65. COROUTINES
    class Manager {
    private $tasks = [];
    function addTask(Task $task) {
    array_unshift($this->tasks, $task);
    }
    function run() {
    while (count($this->tasks)) {
    $next = array_pop($this->tasks);
    $next->run();
    if ($next->valid()) {
    $this->addTask($next);
    }
    }
    }
    }
    

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66. COROUTINES
    $manager = new Manager();
    $manager->addTask(
    new Task(checkRations($people)
    );
    $manager->addTask(
    new Task(watchFences($people, $fences)
    );
    $manager->run();
    // 㱺 checking rations for Lorna
    // 㱺 Lorna is watching next to the old car
    // 㱺 checking rations for Rob
    // 㱺 Rob is watching behind the kennel
    // 㱺 checking rations for Chris
    // 㱺 Chris is watching out back
    // 㱺 checking rations for Aaron
    // 㱺 checking rations for Sara
    

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67. COROUTINES
    $manager = new Manager();
    $manager->addTask(
    new Task(checkRations($people)
    );
    $manager->addTask(
    new Task(watchFences($people, $fences)
    );
    $manager->run();
    // 㱺 checking rations for Lorna
    // 㱺 Lorna is watching next to the old car
    // 㱺 checking rations for Rob
    // 㱺 Rob is watching behind the kennel
    // 㱺 checking rations for Chris
    // 㱺 Chris is watching out back
    // 㱺 checking rations for Aaron
    // 㱺 checking rations for Sara
    

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