The Iterator interface

導入

Interface for external iterators or objects that can be iterated themselves internally.

クラス概要

Iterator

Iterator implements Traversable {

/* Methods */

abstract public mixed current ( void )

abstract public scalar key ( void )

abstract public void next ( void )

abstract public void rewind ( void )

abstract public boolean valid ( void )

}

例1 Basic usage

This example demonstrates in which order methods are called when foreach()ing over an iterator.


<?php
class myIterator implements Iterator {
    private $position = 0;
    private $array = array(
        "firstelement",
        "secondelement",
        "lastelement",
    );  

    public function __construct() {
        $this->position = 0;
    }

    function rewind() {
        var_dump(__METHOD__);
        $this->position = 0;
    }

    function current() {
        var_dump(__METHOD__);
        return $this->array[$this->position];
    }

    function key() {
        var_dump(__METHOD__);
        return $this->position;
    }

    function next() {
        var_dump(__METHOD__);
        ++$this->position;
    }

    function valid() {
        var_dump(__METHOD__);
        return isset($this->array[$this->position]);
    }
}

$it = new myIterator;

foreach($it as $key => $value) {
    var_dump($key, $value);
    echo "\n";
}
?>

上の例の出力は、たとえば以下のようになります。

string(18) "myIterator::rewind"
string(17) "myIterator::valid"
string(19) "myIterator::current"
string(15) "myIterator::key"
int(0)
string(12) "firstelement"

string(16) "myIterator::next"
string(17) "myIterator::valid"
string(19) "myIterator::current"
string(15) "myIterator::key"
int(1)
string(13) "secondelement"

string(16) "myIterator::next"
string(17) "myIterator::valid"
string(19) "myIterator::current"
string(15) "myIterator::key"
int(2)
string(11) "lastelement"

string(16) "myIterator::next"
string(17) "myIterator::valid"


For anyone interested in how exactly does a iterator work in a foreach:



<?php

class SomeIterator implements Iterator {/*...implement...*/}



$it=new SomeIterator();

foreach($it as $key => $val) {

    print "{$key}=>{$val}\n";

}



// works exactly the same as 



$it=new SomeIterator();

for(

    $it->rewind();

    $it->valid();

    $val=$it->current(), $key=$it->key(), $it->next()

) {

    print "{$key}=>{$val}\n";

}



// and if someone forgot how for(;;) works...



$it=new SomeIterator();

$it->rewind;

while($it->valid()) {

    $val=$it->current();

    $key=$it->key();

    $it->next();



    print "{$key}=>{$val}\n";

}

?>

add a note

Iterator::current

Traversable

Last updated: Fri, 30 Jan 2009

The Iterator interface

導入

クラス概要

目次