The document discusses generators and yield in PHP. It begins by explaining generators as a special routine that yields values during iteration to control loop behavior. Generators allow creating iterators without implementing complex iterator interfaces. Examples show how generators can iterate ranges efficiently, transform sequences, chain operations, and select values conditionally. The document also discusses using generators for asynchronous and non-blocking applications by yielding control back to an event loop.

1. Generating
Power with Yield/Jason Myers @jasonamyers

2. Yield, a modern language love
story
Originally Proposed in 1995, the yield keyword became official via the
RFP on June 20th 2013 with PHP 5.5.Generators
Facebook said a Hip, Hop and Don't Stop, and did their own yield
generators in HipHop PHP

3. They are HEAVILY BASED off of Python, with a nod towards the
Mozilla JS implementation and the await C# concept.

6. Iterator
An object that lets us traverse a container

8. PHP Iterator Interface
Iterator extends Traversable {
/* Methods */
abstract public mixed current ( void )
abstract public scalar key ( void )
abstract public void next ( void )
abstract public void rewind ( void )
abstract public boolean valid ( void )
}
For example checkout classArrayIterator

9. ArrayIterator Example
$fruits = array(
"apple" => "yummy",
"orange" => "ah ya, nice",
"grape" => "wow, I love it!",
"plum" => "nah, not me"
);
$obj = new ArrayObject( $fruits );
$it = $obj->getIterator();
echo "Iterating over: " . $obj->count() . " valuesn";
while( $it->valid() )
{
echo $it->key() . "=" . $it->current() . "n";
$it->next();
}
Iterating over: 4 values
apple=yummy
orange=ah ya, nice
grape=wow, I love it!
plum=nah, not me

10. Generator
a special routine that can be used to control the iteration behavior of
a loop, and yields the values one at a time

11. TL;DR
A generator looks like a function but behaves like an iterator

13. Performant?
range(0, 1000000)
Uses over 100MB of RAM

15. Generator Version
function xrange($start, $limit, $step = 1) {
if ($start < $limit) {
if ($step <= 0) {
throw new LogicException('Step must be +ve');
}
for ($i = $start; $i <= $limit; $i += $step) {
yield $i;
}
} else {
if ($step >= 0) {
throw new LogicException('Step must be -ve');
}
for ($i = $start; $i >= $limit; $i += $step) {
yield $i;
}
}
}
uses less than 1KB!

16. TL; DR
function xrange($min, $max) {
for ($i = $min; $i < $max; $i++) {
yield $i;
}
}

17. Sequences
function collatz($val) {
yield $val;
while ($val != 1) {
if ($val%2 == 0) {
$val /= 2;
} else {
$val = 3*$val + 1;
}
yield $val;
}
}
foreach (collatz(11) as $c) {
echo $c," ";
}
11 34 17 52 26 13 40 20 10 5 16 8 4 2 1

19. Y U Only LOOPin?
It will work for any function that takes an Iterator or a Traversable as
argument
$arr = iterator_to_array(collatz(11));

20. Transformations
function multiply_sequence($a, $fac) {
foreach ($a as $val) {
yield $val*$fac;
}
}
function to_html_list($input) {
foreach ($input as $val) {
yield "<li>".$val."</li>";
}
}

21. Chaining
foreach (to_html_list(multiply_sequence(collatz(5),2)) as $val) {
echo $val,"n";
}
<li>10</li>
<li>32</li>
<li>16</li>
<li>8</li>
<li>4</li>
<li>2</li>

22. Selections
function select_pattern($input, $pattern) {
foreach ($input as $val) {
if (preg_match($pattern, $val)) {
yield $val;
}
}
}

23. Breath In
function getLines($file) {
$f = fopen($file, 'r');
if (!$f) {
throw new Exception();
}
while ($line = fgets($f)) {
yield $line;
}
fclose($f);
}
foreach (getLines("someFile") as $line) {
doSomethingWithLine($line);
}

24. Breath Out
function createLog($file) {
$f = fopen($file, 'a');
while (true) {
$line = yield;
fwrite($f, $line);
}
}
$log = createLog($file);
$log->send("First");
$log->send("Second");
$log->send("Third");

26. Bro Remote Me!
Fake the simultaneous processing of data

28. Green Threads
threads that are scheduled by a virtual machine (VM/interperter?)
instead of natively by the underlying operating system

29. function step1() {
$f = fopen("file.txt", 'r');
while ($line = fgets($f)) {
processLine($line);
yield true;
}
}

30. function step2() {
$f = fopen("file2.txt", 'r');
while ($line = fgets($f)) {
processLine($line);
yield true;
}
}

31. function step3() {
$f = fsockopen("www.example.com", 80);
stream_set_blocking($f, false);
$headers = "GET / HTTP/1.1rn";
$headers .= "Host: www.example.comrn";
$headers .= "Connection: Closernrn";
fwrite($f, $headers);
$body = '';
while (!feof($f)) {
$body .= fread($f, 8192);
yield true;
}
processBody($body);
}

32. function runner(array $steps) {
while (true) {
foreach ($steps as $key => $step) {
$step->next();
if (!$step->valid()) {
unset($steps[$key]);
}
}
if (empty($steps)) return;
}
}
runner(array(step1(), step2(), step3()));

33. ZOMG... THERE BE DRAGONS!
This relies on making sure we have no blocking IO

34. overREACTPHP much?
event based, non-blocking IO - ReActPHP

35. One More Thing
So if I can flip control, I can haz an Async?

36. class Buffer {
protected $reads, $data;
public function __construct() {
$this->reads = new SplQueue();
$this->data = new SplQueue();
}
public function read() {
if( $this->data->isEmpty() ) {
$deferred = new ReactPromiseDeferred();
$this->reads->enqueue($deferred->resolver());
return $deferred->promise();
} else {
return ReactPromiseWhen::resolve($this->data->dequeue());
}
}
public function write($str) {
if( $this->reads->isEmpty() ) {
$this->data->enqueue($str);
} else {
$this->reads->dequeue()->resolve($str);
}
}
}

37. function printer(Buffer $buffer) {
while( true ) {
$value = ( yield Util::async($buffer->read()) );
echo "Printer: ", $value, PHP_EOL;
yield Util::async(nested_printer($buffer));
}
}

38. function nested_printer(Buffer $buffer) {
for( $i = 0; $i < 5; $i++ ) {
// Yield a promise task and wait for the result - this is non-blocking
$value = ( yield Util::async($buffer->read()) );
echo "Nested printer: ", $value, PHP_EOL;
}
}

39. $buffer = new Buffer();
$scheduler = new AsyncScheduler();
$scheduler->add(new AsyncTaskGeneratorTask(printer($buffer)));
$i = 0;
$scheduler->add(new AsyncTaskRecurringTask(
function() use($buffer, &$i) { $buffer->write(++$i); }
));
$scheduler->run();
Printer: 1
Nested printer: 2
Nested printer: 3
Nested printer: 4
Nested printer: 5
Nested printer: 6
Printer: 7
Nested printer: 8
Nested printer: 9
Nested printer: 10
Nested printer: 11
Nested printer: 12
...

40. $loop = ReactEventLoopFactory::create();
$scheduler = new AsyncScheduler();
$scheduler->add(new AsyncTaskRecurringTask([$loop, 'tick']));
$scheduler->run();

41. Async
Created by Matt Pryor, on Bitbucket

42. Thanks
Huge thanks to Paul M. Jones and William Golden!

43. THE END
@jasonamyers