Last updated: Fri, 30 Jan 2009

The ArrayAccess interface

導入

Interface to provide accessing objects as arrays.

クラス概要

ArrayAccess

ArrayAccess {

/* Methods */

abstract public boolean offsetExists ( string $offset )

abstract public mixed offsetGet ( string $offset )

abstract public void offsetSet ( string $offset , string $value )

abstract public void offsetUnset ( string $offset )

}

例1 Basic usage


<?php
class obj implements arrayaccess {
    private $container = array();
    public function __construct() {
        $this->container = array(
            "one"   => 1,
            "two"   => 2,
            "three" => 3,
        );
    }
    public function offsetSet($offset, $value) {
        $this->container[$offset] = $value;
    }
    public function offsetExists($offset) {
        return isset($this->container[$offset]);
    }
    public function offsetUnset($offset) {
        unset($this->container[$offset]);
    }
    public function offsetGet($offset) {
        return isset($this->container[$offset]) ? $this->container[$offset] : null;
    }
}

$obj = new obj;

var_dump(isset($obj["two"]));
var_dump($obj["two"]);
unset($obj["two"]);
var_dump(isset($obj["two"]));
$obj["two"] = "A value";
var_dump($obj["two"]);

?>

上の例の出力は、たとえば以下のようになります。

bool(true)
int(2)
bool(false)
string(7) "A value"


Note that at least in PHP 5.1, objects implementing ArrayAccess cannot return objects by reference.  See http://bugs.php.net/bug.php?id=34783 .  If you have code like 



<?php

$x = &$y[0];

?>



then this will (as far as I can tell) *always* fail unless $y is a real array -- it cannot work if $y is an object implementing ArrayAccess.  If your offsetGet() function returns by reference, you get the fatal error "Declaration of MyClass::offsetGet() must be compatible with that of ArrayAccess::offsetGet()".  If you try to have it return by value, however, you get the (contradictory) fatal error "Objects used as arrays in post/pre increment/decrement must return values by reference", at least in my version of PHP.



It is therefore not possible to take arbitrary code dealing with arrays and try to substitute an object of your own for an array, even if all of the normal array functions didn't fail as well (which they do, or at least some of them).

add a note

ArrayAccess::offsetExists

IteratorAggregate::getIterator

Last updated: Fri, 30 Jan 2009

The ArrayAccess interface

導入

クラス概要

目次