PHP Unconference Europe 2015

The SeekableIterator interface

(PHP 5 >= 5.1.0)

Introduction

The Seekable iterator.

Interface synopsis

SeekableIterator extends Iterator {
/* Methods */
abstract public void seek ( int $position )
/* Inherited methods */
abstract public mixed Iterator::current ( void )
abstract public scalar Iterator::key ( void )
abstract public void Iterator::next ( void )
abstract public void Iterator::rewind ( void )
abstract public boolean Iterator::valid ( void )
}

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();
}
?>

The above example will output something similar to:

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

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User Contributed Notes 5 notes

up
4
svenr at selfhtml dot org
2 years ago
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
 
}
}

?>
up
0
Anonymous
1 year ago
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)");
}
?>
up
0
martin at smasty dot net
3 years ago
The reflection approach:

<?php

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

?>
up
0
marcin dot kleczek at gmail dot com
4 years ago
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
up
-3
dreake at example dot com
5 years ago
This example show how to check if some class has method seek() (or another method).

<?php
$class
= 'SeekableIterator';
           
$findingMethod = 'seek'; // have to be lower chars
           
           
$methods = get_class_methods($class);
           
            for(
$i = 0, $ii = count($methods); $i < $ii; $i++){
               
$sl = strtolower($methods[$i]);
               
$lowermethods[$i] = $sl;
            }
           
           
            if(
in_array($findingMethod,$lowermethods))
                echo
'This class has method seek().';
?>
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