The SeekableIterator interface

(PHP 5 >= 5.1.0, PHP 7)

简介

The Seekable iterator.

接口摘要

SeekableIterator extends Iterator {
/* 方法 */
abstract public seek ( int $position ) : void
/* 继承的方法 */
abstract public Iterator::current ( void ) : mixed
abstract public Iterator::key ( void ) : scalar
abstract public Iterator::next ( void ) : void
abstract public Iterator::rewind ( void ) : void
abstract public Iterator::valid ( void ) : bool
}

Example #1 Basic usage

This example demonstrates creating a custom SeekableIterator, seeking to a position and handling an invalid position.

<?php
class MySeekableIterator implements SeekableIterator {

    private $position;

    private $array = array(
        "first element",
        "second element",
        "third element",
        "fourth element"
    );

    /* Method required for SeekableIterator interface */

    public function seek($position) {
      if (!isset($this->array[$position])) {
          throw new OutOfBoundsException("invalid seek position ($position)");
      }

      $this->position = $position;
    }

    /* Methods required for Iterator interface */
    
    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();
}
?>

以上例程的输出类似于：

first element
third element
second element
invalid seek position (10)

Table of Contents

User Contributed Notes

Anonymous 20-Oct-2013 12:43
The code above is missing a closing parenthesis.

<?php
if (!isset($this->array[$position]) {
          throw new OutOfBoundsException("invalid seek position ($position)");
}
?>

should be

<?php
if (!isset($this->array[$position])) { // close here
          throw new OutOfBoundsException("invalid seek position ($position)");
}
?>
svenr at selfhtml dot org 14-Nov-2011 04:21
Best method:

<?php

if ($object instanceof SeekableIterator) {
  echo "\$object has method seek()";
}

?>

Please, make use of checking if a particular interface has been implemented to assure that the object you are dealing with definately has the methods you are about to use.

This also works as typehinting:

<?php

class foo {
  public function doSomeSeeking(SeekableIterator $seekMe) {
    $seekMe->seek(10); // will work, otherwise Typehint triggers complaints
  }
}

?>
martin at smasty dot net 15-May-2011 08:01
The reflection approach:

<?php

$reflection = new ReflectionClass('MySeekableIterator');
if($reflection->hasMethod('seek'))
  echo "This class has method seek().";

?>
marcin dot kleczek at gmail dot com 15-Apr-2010 11:59
Better method:

<?php
            $class = 'SeekableIterator';
            $findingMethod = 'seek'; // have to be lower chars
          
            $methods = get_class_methods($class);
          
            foreach( $methods as $pVal )
                if ( $findingMethod == strtolower($pVal) ) {
                    echo 'This class has method seek().';
                    break;
                }

}

?>

Best method: http://php.net/manual/en/function.method-exists.php