The document discusses various PHP concepts including iterators, generators, arrays, and performance. It provides examples of using iterators, generators, and default array functions to iterate over arrays and collections. It also compares the readability and performance of these different approaches. The document suggests that generators can help avoid memory issues by evaluating sequences lazily without building entire arrays in memory.

1. SEMANTIC WEAPONS
PHP Conf 2016
HELLO STRANGER

2. SEMANTIC WEAPONS
$ id -un
– carlos@semantic.mx
– tweet me @cvences
– Founded a 4yo development shop
– semanticweapons.com
#phpconmx

3. and we’re hiring!
HELLO STRANGER
SEMANTIC WEAPONS

4. SEMANTIC WEAPONS
PHP for Python Developers

5. SEMANTIC WEAPONS
PHP for Python Developers
Web Development & General Scripting

6. SEMANTIC WEAPONS
$ membership operator _
$inArray = in_array(5, range(0, 10)) === TRUE;

7. SEMANTIC WEAPONS
$ membership operator _
in_array = 5 in range(10) == True

8. SEMANTIC WEAPONS
$ membership operator _
in_array = 5 in range(10) == True
>>> in_array
False

9. SEMANTIC WEAPONS
$ default values _
# counting dictionary keys
from collections import defaultdict
log = ['warn', 'error', 'debug', 'info', 'warn', 'debug', 'warn']
stats = defaultdict(int)
for entry in log:
stats[entry] += 1

10. SEMANTIC WEAPONS
$ default values _
// counting elements
$log = ['warn', 'error', 'debug', 'info', 'warn', 'debug', ‘warn'];
$stats = [];
foreach ($log as $entry){
$stats[$entry] = $stats[$entry]++ ?: 0;
}

11. SEMANTIC WEAPONS
$ default values _
// counting elements
$log = ['warn', 'error', 'debug', 'info', 'warn', 'debug', ‘warn'];
$stats = [];
foreach ($log as $entry){
$stats[$entry]++;
}

12. SEMANTIC WEAPONS
$ default values _
// counting elements
$log = ['warn', 'error', 'debug', 'info', 'warn', 'debug', ‘warn'];
$stats = [];
foreach ($log as $entry){
$stats[$entry]++;
}
# counting dictionary keys
from collections import defaultdict
log = ['warn', 'error', 'debug', 'info', 'warn', 'debug', ‘warn']
stats = defaultdict(int)
for entry in log:
stats[entry] += 1

13. SEMANTIC WEAPONS
Memory consumption
– C’s pointers
– SQL’s LIMIT statement
– strcmp, strcpy, strcat
– strncmp, strncpy, strncat
– buffer overflow

14. SEMANTIC WEAPONS
Memory consumption
– C’s pointers
– SQL’s LIMIT statement
– strcmp, strcpy, strcat
– strncmp, strncpy, strncat
– buffer overflow
¿Quién agregó
la clausula LIMIT
a mini SQL 1.x?

15. SEMANTIC WEAPONS
$ Array
function myRange($max = 10) {
$numeros = [];
$num = 1;
while ($num < $max) {
array_push($numeros, $num);
$num++;
}
return $numeros;
}
function sum($max = 10) {
$sumatoria = 0;
foreach (myRange($max) as $num) {
$sumatoria += $num;
}
echo $sumatoria;
}
sum(1000000);

16. SEMANTIC WEAPONS
$ Iterator
class NumberIter implements Iterator {
private $position = 0;
private $array = [];
public function __construct($array = []) {
$this->position = 0;
$this->array = $array;
}
public function rewind() {
$this->position = 0;
}
public function current() {
return $this->array[$this->position];
}
public function key() {
return $this->position;
}
public function next() {
++$this->position;
}
public function valid() {
return isset($this->array[$this->position]);
}
}
function sum($max = 10) {
$sumatoria = 0;
$numberIter = new NumberIter($array = range(1, ($max - 1)));
foreach ($numberIter as $num) {
$sumatoria += $num;
}
echo $sumatoria;
}
sum(1000000);

17. SEMANTIC WEAPONS
$ PHP Arrays vs Iterators
foreach (myRange($max) as $num) {
$sumatoria += $num;
}
foreach ($numberIter as $num) {
$sumatoria += $num;
}

18. SEMANTIC WEAPONS
Entering
Generators

19. SEMANTIC WEAPONS
$ Generators
function myRange($max = 10) {
// $numeros = [];
$num = 1;
while ($num < $max) {
yield $num;
$num++;
}
// return $numeros;
}
function sum($max = 10) {
$sumatoria = 0;
foreach (myRange($max) as $num) {
$sumatoria += $num;
}
echo $sumatoria;
}
sum(1000000);

20. SEMANTIC WEAPONS
Generators
– Implement Iterators
– DRY
– Can traverse with foreach
– foreach does not use IAP (>7.0.0)
– Uses hashtable iterators now
– Does not build an array in-memory
– Also speeds time to generate
Note: – Calling range(0, 1000000) will result in well over 100 MB of memory being used.

21. SEMANTIC WEAPONS
$ Iterators, Generators and Arrays
class NumberIter implements Iterator {
private $position = 0;
private $array = [];
public function __construct($array = []) {
$this->position = 0;
$this->array = $array;
}
public function rewind() {
$this->position = 0;
}
public function current() {
return $this->array[$this->position];
}
public function key() {
return $this->position;
}
public function next() {
++$this->position;
}
public function valid() {
return isset($this->array[$this->position]);
}
}
function myRange($max = 10) {
$num = 1;
while ($num < $max) {
yield $num;
$num++;
}
}
array range ($start, $end, $step)

22. SEMANTIC WEAPONS
$ Iterators, Generators and Arrays
class NumberIter implements Iterator {
private $position = 0;
private $array = [];
public function __construct($array = []) {
$this->position = 0;
$this->array = $array;
}
public function rewind() {
$this->position = 0;
}
public function current() {
return $this->array[$this->position];
}
public function key() {
return $this->position;
}
public function next() {
++$this->position;
}
public function valid() {
return isset($this->array[$this->position]);
}
}
function myRange($max = 10) {
$num = 1;
while ($num < $max) {
yield $num;
$num++;
}
}

23. SEMANTIC WEAPONS
Case of Study

24. SEMANTIC WEAPONS
$ PHP 7.1.0 RC2_

25. SEMANTIC WEAPONS
Using Generators

26. SEMANTIC WEAPONS
$ PHP 7.1.0 RC2_

27. SEMANTIC WEAPONS
Using Iterators

28. SEMANTIC WEAPONS
HELLO STRANGER
PHP 7.1.0 RC2

29. SEMANTIC WEAPONS
$ time

30. SEMANTIC WEAPONS
To be or not to be
– Using iterators is great
– foreach in 7.0.0 rocks!
– lists are fat, sequences evaluate lazily
– Lazy is good

31. SEMANTIC WEAPONS
Warning: sort() expects parameter 1 to be array, object given

32. SEMANTIC WEAPONS
But…
– Python iterators introduced in 2.2 (2001)
– range -> xrange -> range
– PHP yield introduced in 5.5.0+ (2013)
– Iterator name space may clash
– What’s wrong with iterator_to_array?
– PHP ArrayAccess
Blog Post: SPL Iterators against the performance
PHP Manual: /language.generators.overview.php

33. SEMANTIC WEAPONS
Readability

34. SEMANTIC WEAPONS
$ unpacking a list _
sum_of_numbers = sum([x**3 for x in range(10000)])

35. SEMANTIC WEAPONS
$ unpacking an array _
$sumOfNumbers = 0;
foreach (range(1, 10000) as $num) {
$sumOfNumbers += pow($num, 3);
}

36. SEMANTIC WEAPONS
$ unpacking an array _
// second try
$processArray = function($method, $array) {
return array_map($method, $array);
};
$sumOfNumbers = array_sum(
$processArray(
$method = function($x){return pow($x, 3);},
$array = range(0, 10000)
)
);

37. SEMANTIC WEAPONS
One liners
– means something in English
– easy to understand at first glance

38. SEMANTIC WEAPONS
$ unpacking an array _
$sumOfNumbers = 0;
foreach (range(1, 10000) as $value) {
$sumOfNumbers += pow($value, 3);
}
// second try
$processArray = function($method, $array) {
return array_map($method, $array);
};
$sumOfNumbers = array_sum(
$processArray(
$method = function($x){return pow($x, 3);},
$array = range(0, 10000)
)
);
// third try
$sumOfNumbers = array_sum(array_map(function($x){return pow($x, 3);}, range(0, 10000)));

39. SEMANTIC WEAPONS
$ readability _
sum_of_numbers = sum([x**3 for x in range(10000)])
$y = array_sum(array_map(function($x){return pow($x, 3);}, range(0, 10000)));

40. SEMANTIC WEAPONS
$ looping over two collections _
speakers = ['Javier', 'Joe', 'Rasmus', 'Carlos']
talks = ['Ansible', 'Loopless', 'Deploy', 'Python']
for speaker, talk in zip(speakers, talks):
print(speaker, talk)

41. SEMANTIC WEAPONS
$ looping over two collections _
$speakers = ['Javier', 'Joe', 'Rasmus', 'Carlos'];
$talks = ['Ansible', 'Loopless', 'Deploy', 'Python'];
$max = min(count($speakers), count($talks));
foreach(range(0, $max-1) as $i){
echo($speakers[$i] .' '. $talks[$i]);
}

42. SEMANTIC WEAPONS
$ looping over two collections _
// second approach
$speakers = ['Javier', 'Joe', 'Rasmus', 'Carlos'];
$talks = ['Ansible', 'Loopless', 'Deploy', 'Python'];
$meetupTalks = array_combine($speakers, $talks);
foreach($meetupTalks as $speaker => $talk){
echo "$speaker $talk";
}

43. SEMANTIC WEAPONS
$ looping over two collections _
for speaker, talk in zip(speakers, talks):
print(speaker, talk)
foreach(array_combine($speakers, $talks) as $speaker => $talk)
echo "$speaker $talk";

44. SEMANTIC WEAPONS
$ python iterators magic, tweet .@cvences
# dado un array asociativo, elimina todos los nombres que empiecen con la letra “c”
meetup_info = {
'Javier': 'Ansible',
'Joe': 'Loopsless',
'Rasmus': 'Deploy',
'Carlos': 'Python',
}
meetup_info = {key: meetup_info[key] for key in meetup_info if not key.lower().startswith('c')}
# dado un modelo con relationships, filtra los blogs cuyos autores tengan o no
# un nombre asignado. El título no incluye la palabra python y ordénalos por fecha
# de creación descendente.
Blog.objects
.filter(entry__authors__isnull=False, entry__authors__name__isnull=True)
.exclude(entry__title__icontains=‘python’)
.order_by(‘-created’)

45. SEMANTIC WEAPONS
$ python iterators magic
def fib(n):
return (4 << n * (3 + n)) // ((4 << 2 * n) - (2 << n) - 1) & ((2 << n) - 1)
def get_fibonacci_by_position(pos):
"""
Returns the fibonacci number at pos
"""
a, b = 1, 1
for _ in range(pos):
a, b = a + b, a
return b

47. carlos@semantic.mx
HELLO STRANGER
SEMANTIC WEAPONS