Detailed explanation of the interface of PHP SPL standard library_PHP tutorial

Detailed explanation of the interface (Interface) of the PHP SPL standard library

This article mainly introduces the detailed explanation of the interface (Interface) of the PHP SPL standard library. This article explains the Coutable interface and OuterIterator respectively. Interface, RecursiveIterator interface, SeekableIterator interface, SplObserver and SplSubject interface, etc. Friends in need can refer to it

PHP SPL standard library has a total of 6 interfaces, as follows:

　1.Countable

　2.OuterIterator

　3.RecursiveIterator

4.SeekableIterator

　5.SplObserver

　6.SplSubject

Among them, OuterIterator, RecursiveIterator, and SeekableIterator all inherit the Iterator class. The function and use of each interface will be explained in detail below.

Coutable interface:

Objects that implement the Countable interface can be used for counting with the count() function.

The code is as follows:

class Mycount implements Countable

　{

public function count()

　{

static $count = 0;

　$count ;

return $count;

　}

　}

　$count = new Mycount();

　$count->count();

　$count->count();

echo count($count); //3

echo count($count); //4

Description:

When calling the count() function, the Mycount::count() method is called

The second parameter of the count() function will have no effect

OuterIterator interface:

Customize or modify the iteration process.

The code is as follows:

//IteratorIterator is an implementation class of OuterIterator

class MyOuterIterator extends IteratorIterator {

public function current()

　{

return parent::current() . 'TEST';

　}

　}

　foreach(new MyOuterIterator(new ArrayIterator(['b','a','c'])) as $key => $value) {

echo "$key->$value".PHP_EOL;

　}

　/*

Result:

　0->bTEST

　1->aTEST

　2->cTEST

　*/

In practical applications, OuterIterator is extremely useful:

The code is as follows:

$db = new PDO('mysql:host=localhost;dbname=test', 'root', 'mckee');

　$db->query('set names utf8');

$pdoStatement = $db->query('SELECT * FROM test1', PDO::FETCH_ASSOC);

　$iterator = new IteratorIterator($pdoStatement);

　$tenRecordArray = iterator_to_array($iterator);

print_r($tenRecordArray);

RecursiveIterator interface:

Used to iterate multi-layer data in a loop, RecursiveIterator provides two additional methods:

RecursiveIterator::getChildren Gets the child iterator of the current element

RecursiveIterator::hasChildren determines whether there is an iterator under the current element

The code is as follows:

class MyRecursiveIterator implements RecursiveIterator

　{

private $_data;

private $_position = 0;

public function __construct(array $data) {

$this->_data = $data;

　}

public function valid() {

return isset($this->_data[$this->_position]);

　}

public function hasChildren() {

return is_array($this->_data[$this->_position]);

　}

public function next() {

　$this->_position ;

　}

public function current() {

return $this->_data[$this->_position];

　}

public function getChildren() {

print_r($this->_data[$this->_position]);

　}

public function rewind() {

　$this->_position = 0;

　}

public function key() {

return $this->_position;

　}

　}

　$arr = array(0, 1=> array(10, 20), 2, 3 => array(1, 2));

$mri = new MyRecursiveIterator($arr);

foreach ($mri as $c => $v) {

　if ($mri->hasChildren()) {

echo "$c has children: " .PHP_EOL;

$mri->getChildren();

　} else {

echo "$v" .PHP_EOL;

　}

　}

　/*

Result:

　0

　1 has children:

Array

　(

　[0] => 10

　[1] => 20

　)

　2

　3 has children:

Array

　(

　[0] => 1

　[1] => 2

　)

　*/

SeekableIterator interface:

Implement a searchable iterator through the seek() method, which is used to search for elements at a certain position.

The code is as follows:

　　class MySeekableIterator implements SeekableIterator {

　　private $position = 0;

　　private $array = array(

　　"first element" ,

　　"second element" ,

　　"third element" ,

　　"fourth element"

　　);

　　public function seek ( $position ) {

　　if (!isset( $this -> array [ $position ])) {

　　throw new OutOfBoundsException ( "invalid seek position ( $position )" );

　　}

　　$this -> position = $position ;

　　}

　　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 ]);

　　}

　　}

　　try {

　　$it = new MySeekableIterator ;

　　echo $it -> current (), "n" ;

　　$it -> seek ( 2 );

　　echo $it -> current (), "n" ;

　　$it -> seek ( 1 );

　　echo $it -> current (), "n" ;

　　$it -> seek ( 10 );

　　} catch ( OutOfBoundsException $e ) {

　　echo $e -> getMessage ();

　　}

　　/*

　　结果：

　　first element

　　third element

　　second element

　　invalid seek position ( 10 )

　　*/

　　SplObserver和SplSubject接口:

　　SplObserver和SplSubject接口用来实现观察者设计模式，观察者设计模式是指当一个类的状态发生变化时，依赖它的对象都会收到通知并更新。使用场景非常广泛，比如说当一个事件发生后，需要更新多个逻辑操作，传统方式是在事件添加后编写逻辑，这种代码耦合并难以维护，观察者模式可实现低耦合的通知和更新机制。

　　看看SplObserver和SplSubject的接口结构：

　　 代码如下:

　　//SplSubject结构 被观察的对象

　　interface SplSubject{

　　public function attach(SplObserver $observer); //添加观察者

　　public function detach(SplObserver $observer); //剔除观察者

　　public function notify(); //通知观察者

　　}

　　//SplObserver结构 代表观察者

　　interface SplObserver{

　　public function update(SplSubject $subject); //更新操作

　　}

　　看下面一个实现观察者的例子：

　　复制代码 代码如下:

　　class Subject implements SplSubject

　　{

　　private $observers = array();

　　public function attach(SplObserver $observer)

　　{

　　$this->observers[] = $observer;

　　}

　　public function detach(SplObserver $observer)

　　{

　　if($index = array_search($observer, $this->observers, true)) {

　　unset($this->observers[$index]);

　　}

　　}

　　public function notify()

　　{

　　foreach($this->observers as $observer) {

　　$observer->update($this);

　　}

　　}

　　}

　　class Observer1 implements SplObserver

　　{

　　public function update(SplSubject $subject)

　　{

　　echo "逻辑1代码".PHP_EOL;

　　}

　　}

　　class Observer2 implements SplObserver

　　{

　　public function update(SplSubject $subject)

　　{

　　echo "逻辑2代码".PHP_EOL;

　　}

　　}

　　$subject = new Subject();

　　$subject->attach(new Observer1());

　　$subject->attach(new Observer2());

　　$subject->notify();

　　/*

　　结果：

　　逻辑1代码

　　逻辑2代码

　　*/

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