Uncovering Iterators

Uncovering Iterators
SJORS DE VALK
25 NOVEMBER 2010

ITERATORS (1)
∂ Black magic?

ITERATORS (3)
“An iterator is an object that allows a programmer
to traverse through all the elements of a
collection.”
∂ Wikipedia

ITERATORS (4)
$i = array(1, 2, 3);
reset($i);
while (current($i) !== false) {
echo key($values), current($values);
next($values);
}
∂ Array iteration (old school)

ITERATORS (5)
$i = new MyIterator();
$i->rewind();
while ($i->valid()) {
echo $i->key(), $i->current();
$i->next();
}

ITERATORS (6)
 rewind()
 valid()
 key()
 current()
 next()
∂ As deﬁned by the Iterator interface

ITERATORS (7)
$i = new MyIterator();
foreach ($i as $key => $value) {
echo $key, $value;
}
∂ Methods are called automatically

BASICS (1)
$values = array(
‘Cameron Diaz’,
‘Alizée Jacotey’,
‘Britney Spears’,
‘Penélope Cruz’
);

BASICS (2)
class NaiveWomenIterator implements Iterator {
function __construct(array $values) {...}
function rewind() {...}
function valid() {...}
function key() {...}
function current() {...}
function next() {...}
}

BASICS (3)
class WomenIterator extends ArrayIterator {
// Nothing here
}
∂ Lean and mean

BASICS (4)
$i = new WomenIterator($values);
$i = new WomenFilterIterator($i);
foreach ($i as $name) {
echo $name;
}

BASICS (5)
class WomenFilterIterator extends FilterIterator {
function accept() {
return strpos($this->current(), ‘z’) !== false;
}
}

FIBONACCI (1)
Fibonacci sequence:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144...

FIBONACCI (2)
$previous = 1;
$current = 0;
while (true) {
echo $current;
$oldCurrent = $current;
$current += $previous;
$previous = $oldCurrent;
}
∂ Classic approach

FIBONACCI (3)
$i = new FibonacciIterator();
foreach ($i as $value) {
echo $value;
}
∂ Iterator approach: hides the implementation

FIBONACCI (4)
$i = new FibonacciIterator();
$i = new LimitIterator($i, 0, 50);
foreach ($i as $value) {
echo $value;
}
∂ No need to change the original iterator

WORDS (1)
$contents = loadFile(‘http://www.gutenberg…’);
$i = new NaiveWordIterator($contents);
foreach ($i as $word) {
echo $word;
}

WORDS (2)
$i = new CharacterIterator($contents);
$i = new WordIterator($i);
echo $word;
}

WORDS (3)
$i = new RegexIterator($i, ‘/god/i’);
echo $word;
}

WORDS (4)
$i = new RegexIterator($i, ‘/god/i’);
$i = new BigWordsFilterIterator($i, 5);
echo $word;
}

WORDS (5)
$i = new WordFrequencyIterator($i);
echo $word;
}

WORDS (6)
$i = new BigWordsFilterIterator($i, 10);
$i = new WordFrequencyIterator($i);
echo $word;
}

MP3 (1)
∂ Old school recursive directory iteration
function listFiles($path) {
$files = array();
$handle = opendir($path);
while (false !== ($file = readdir($handle))) {
$files[] = $file;
if (is_dir($path . ‘/’ . $file)) {
$files = array_merge($files, listFiles($path . ‘/’ . $file));
}
}
return $files;
}

MP3 (2)
∂ Lean and mean. Returns SplFileInfo
$i = new Mp3RecursiveDirectoryIterator($path);
foreach ($i as $ﬁle) {
echo $ﬁle->getFilename();
}

MP3 (3)
function render(Iterator $i) {
echo $i->getDepth(), $i->getFilename();
return true;
}
iterator_apply($i, ‘render’, array($i));

MP3 (4)
echo count($i); // Nope
echo $i->count(); // Nope
echo iterator_count($i);

MP3 (5)
$i = new SongsIterator($i);
foreach ($i as $song) {
echo $song->title;
}

MP3 (6)
$i = new SongsIterator($i);
foreach ($i as $song) {
foreach ($song as $property) {
echo $property; // E.g. title, artist
}
}

MP3 (7)
∂ No need for a toArray()
class Song implements IteratorAggregate {
function getIterator() {
return new ArrayIterator(
get_object_vars($this)
);
}
}

MP3 (8)
$i = new Mp3ShortSongsFilterIterator($i);
}

MP3 (9)
$i = new Mp3ShortSongsFilterIterator($i);
$i = new InﬁniteIterator($i);
}

MOVIES (1)
$i = new ImdbTopMoviesIterator();
foreach ($i as $movie) {
echo $movie->rank, $movie->title;
}

MOVIES (2)
$i = new ImdbBoxOfﬁceMoviesIterator($url);
foreach ($i as $movie) {
echo $movie->rank, $movie->title;
}

MOVIES (3)
$x = new ImdbTopMoviesIterator();
$x = new LimitIterator($x, 1, 10);
$y= new ImdbBoxOfﬁceMoviesIterator($url);
$y = new LimitIterator($y, 1, 10);
$i = new MultipleIterator();
$i->attachIterator($x);
$i->attachIterator($y);

Uncovering Iterators

More Related Content

What's hot (20)

Similar to Uncovering Iterators (20)

Recently uploaded (20)

Uncovering Iterators