It bit me today, so putting it here in the hope it will help others:
If you call array_key_exists() on an object of a class that implements ArrayAccess, ArrayAccess::offsetExists() wil NOT be called.
(PHP 5, PHP 7, PHP 8)
Interface to provide accessing objects as arrays.
Example #1 Basic usage
<?php
class Obj implements ArrayAccess {
public $container = [
"one" => 1,
"two" => 2,
"three" => 3,
];
public function offsetSet($offset, $value): void {
if (is_null($offset)) {
$this->container[] = $value;
} else {
$this->container[$offset] = $value;
}
}
public function offsetExists($offset): bool {
return isset($this->container[$offset]);
}
public function offsetUnset($offset): void {
unset($this->container[$offset]);
}
public function offsetGet($offset): mixed {
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"]);
$obj[] = 'Append 1';
$obj[] = 'Append 2';
$obj[] = 'Append 3';
print_r($obj);
?>The above example will output something similar to:
bool(true)
int(2)
bool(false)
string(7) "A value"
obj Object
(
[container:obj:private] => Array
(
[one] => 1
[three] => 3
[two] => A value
[0] => Append 1
[1] => Append 2
[2] => Append 3
)
)
It bit me today, so putting it here in the hope it will help others:
If you call array_key_exists() on an object of a class that implements ArrayAccess, ArrayAccess::offsetExists() wil NOT be called.<?php
/**
* ArrayAndObjectAccess
* Yes you can access class as array and the same time as object
*
* @author Yousef Ismaeil <cliprz@gmail.com>
*/
class ArrayAndObjectAccess implements ArrayAccess {
/**
* Data
*
* @var array
* @access private
*/
private $data = [];
/**
* Get a data by key
*
* @param string The key data to retrieve
* @access public
*/
public function &__get ($key) {
return $this->data[$key];
}
/**
* Assigns a value to the specified data
*
* @param string The data key to assign the value to
* @param mixed The value to set
* @access public
*/
public function __set($key,$value) {
$this->data[$key] = $value;
}
/**
* Whether or not an data exists by key
*
* @param string An data key to check for
* @access public
* @return boolean
* @abstracting ArrayAccess
*/
public function __isset ($key) {
return isset($this->data[$key]);
}
/**
* Unsets an data by key
*
* @param string The key to unset
* @access public
*/
public function __unset($key) {
unset($this->data[$key]);
}
/**
* Assigns a value to the specified offset
*
* @param string The offset to assign the value to
* @param mixed The value to set
* @access public
* @abstracting ArrayAccess
*/
public function offsetSet($offset,$value) {
if (is_null($offset)) {
$this->data[] = $value;
} else {
$this->data[$offset] = $value;
}
}
/**
* Whether or not an offset exists
*
* @param string An offset to check for
* @access public
* @return boolean
* @abstracting ArrayAccess
*/
public function offsetExists($offset) {
return isset($this->data[$offset]);
}
/**
* Unsets an offset
*
* @param string The offset to unset
* @access public
* @abstracting ArrayAccess
*/
public function offsetUnset($offset) {
if ($this->offsetExists($offset)) {
unset($this->data[$offset]);
}
}
/**
* Returns the value at specified offset
*
* @param string The offset to retrieve
* @access public
* @return mixed
* @abstracting ArrayAccess
*/
public function offsetGet($offset) {
return $this->offsetExists($offset) ? $this->data[$offset] : null;
}
}
?>
Usage
<?php
$foo = new ArrayAndObjectAccess();
// Set data as array and object
$foo->fname = 'Yousef';
$foo->lname = 'Ismaeil';
// Call as object
echo 'fname as object '.$foo->fname."\n";
// Call as array
echo 'lname as array '.$foo['lname']."\n";
// Reset as array
$foo['fname'] = 'Cliprz';
echo $foo['fname']."\n";
/** Outputs
fname as object Yousef
lname as array Ismaeil
Cliprz
*/
?>You might be wondering whether implementing an ArrayAccess interface makes the class iterable. It is, after all, an "array". The answer is no, it doesn't. Additionally there are a couple of subtle gotchas if you add both and want it to be an associate array. The below is a class that has both ArrayAccess AND Iterator interfaces. And Countable as well just to be complete.
<?php
//This uses return types which are only valid in PHP 7. They can be removed if you are forced to use an older version of PHP.
//N.b. The offsetSet method contains a function that is only valid from PHP 7.3 onwards.
class HandyClass implements ArrayAccess, Iterator, Countable {
private $container = array(); //An Array of your actual values.
private $keys = array(); //We use a separate array of keys rather than $this->position directly so that we can
private $position; //have an associative array.
public function __construct() {
$position = 0;
$this->container = array( //Arbitrary array for demo. You probably want to set this to empty in practice or
"a" => 1, //get it from somewhere else, e.g. passing it into the constructor.
"b" => 2,
"c" => 3,
);
$this->keys = array_keys($this->container);
}
public function count() : int { //This is necessary for the Countable interface. It could as easily return
return count($this->keys); //count($this->container). The number of elements will be the same.
}
public function rewind() { //Necessary for the Iterator interface. $this->position shows where we are in our list of
$this->position = 0; //keys. Remember we want everything done via $this->keys to handle associative arrays.
}
public function current() { //Necessary for the Iterator interface.
return $this->container[$this->keys[$this->position]];
}
public function key() { //Necessary for the Iterator interface.
return $this->keys[$this->position];
}
public function next() { //Necessary for the Iterator interface.
++$this->position;
}
public function valid() { //Necessary for the Iterator interface.
return isset($this->keys[$this->position]);
}
public function offsetSet($offset, $value) { //Necessary for the ArrayAccess interface.
if(is_null($offset)) {
$this->container[] = $value;
$this->keys[] = array_key_last($this->container); //THIS IS ONLY VALID FROM php 7.3 ONWARDS. See note below for alternative.
} else {
$this->container[$offset] = $value;
if(!in_array($offset, $this->keys)) $this->keys[] = $offset;
}
}
public function offsetExists($offset) {
return isset($this->container[$offset]);
}
public function offsetUnset($offset) {
unset($this->container[$offset]);
unset($this->keys[array_search($offset,$this->keys)]);
$this->keys = array_values($this->keys); //This line re-indexes the array of container keys because if someone
} //deletes the first element, the rewind to position 0 when iterating would
//cause no element to be found.
public function offsetGet($offset) {
return isset($this->container[$offset]) ? $this->container[$offset] : null;
}
}
?>
Example usages:
<?php
$myClass = new HandyClass();
echo('Number of elements: ' . count($myClass) . "\n\n");
echo("Foreach through the built in test elements:\n");
foreach($myClass as $key => $value) {
echo("$value\n");
}
echo("\n");
$myClass['d'] = 4;
$myClass['e'] = 5;
echo('Number of elements after adding two: ' . count($myClass) . "\n\n");
unset($myClass['a']);
echo('Number of elements after removing one: ' . count($myClass) . "\n\n");
echo("Accessing an element directly:\n");
echo($myClass['b'] . "\n\n");
$myClass['b'] = 5;
echo("Foreach after changing an element:\n");
foreach($myClass as $key => $value) {
echo("$value\n");
}
echo("\n");
?>The indexes used in an ArrayAccess object are not limited to strings and integers as they are for arrays: you can use any type for the index as long as you write your implementation to handle them. This fact is exploited by the SplObjectStorage class.Although $offset can be anything, a string that looks like an integer is cast to integer before the call to any of the methods.
$x[1] offset is integer 1
$x['1'] offset is integer 1
$x['1.'] offset is string '1.'An experimental check addition to the findings of Per (on offsetExists method) added here (8 years ago).
<?php
class obj implements ArrayAccess {
private $container = array();
public function __construct() {
$this->container = array(
"one" => 1,
"two" => 2,
"three" => 3,
);
}
public function offsetSet($offset, $value) {
print "offsetSet method Triggered";
if (is_null($offset)) {
$this->container[] = $value;
} else {
$this->container[$offset] = $value;
}
}
public function offsetExists($offset) {
print "offsetExists method Triggered";
return isset($this->container[$offset]);
}
public function offsetUnset($offset) {
print "offsetUnset method Triggered";
unset($this->container[$offset]);
}
public function offsetGet($offset) {
print "offsetGet method Triggered";
return isset($this->container[$offset]) ? $this->container[$offset] : null;
}
}
$obj = new obj;
## Assigning a Value
$obj['two'] = '2'; // Output: offsetSet method Triggered
## Checking if array offset already set
isset($obj['two']); // Output : offsetExists method Triggered
## Unsetting array value on the offset 'two'
unset($obj['two']); // Output : offsetUnset method Triggered
## Accessing array value at offset 'two'
return $obj['two']; // Output : offsetGet method Triggered
?>Sadly you cannot assign by reference with the ArrayAccess (at least in PHP 5.3.23)
It's too bad there is no syntax for optionally passing variables by reference to functions (a feature in retro PHP).
That option would have let ArrayAccess fully mimic the functionality of normal array assignments:
<?php
$var = 'hello';
$arr = array();
$arr[0] = $var;
$arr[1] = &$var;
$var = 'world';
var_dump($arr[0], $arr[1]);
// string(5) "hello"
// string(5) "world"
?>
Declaring "function offsetSet($offset, &$value)" will cause a fatal error.
So to assign by ref you can use an ugly function call, for example:
<?php
class obj implements ArrayAccess {
// ... ArrayAccess example code ...
public function &offsetSetRef($offset, &$value) {
if (is_null($offset)) {
$this->container[] = &$value;
} else {
$this->container[$offset] = &$value;
}
return $value; // should return in case called within an assignment chain
}
}
$var = 'hello';
$obj = new obj();
$obj[0] = $var;
//$obj[1] = &$var; // Fatal error: Cannot assign by reference to overloaded object
$obj->offsetSetRef(1, $var); // the work around
$var = 'world';
var_dump($obj[0], $obj[1]);
// string(5) "hello"
// string(5) "world"
?>reset() method may not work as you expect with ArrayAccess objects.
Using reset($myArrayAccessObject) returns the first property from $myArrayAccessObject, not the first item in the items array.
If you want to use the reset() method to return the first array item, then you can use the following simple workaround:
<?php
class MyArrayAccessObject implements Iterator, ArrayAccess, Countable {
protected $first = null; //WARNING! Keep this always first.
protected $items = null;
private function supportReset() {
$this->first = reset($this->items); //Support reset().
}
// ...
public function offsetSet($offset, $value) {
if ($offset === null) {
$this->items[] = $value;
}
else {
$this->items[$offset] = $value;
}
$this->supportReset();
}
}
?>
Finally, call $this->supportReset() in the end of all methods that change the internal $items array, such as in offsetSet(), offsetUnset() etc.
This way, you can use the reset() method as normally:
<?php
$firstArrayItem = reset($myArrayAccessObject);
?>Objects implementing ArrayAccess may return objects by references in PHP 5.3.0.
You can implement your ArrayAccess object like this:
class Reflectable implements ArrayAccess {
public function set($name, $value) {
$this->{$name} = $value;
}
public function &get($name) {
return $this->{$name};
}
public function offsetGet($offset) {
return $this->get($offset);
}
public function offsetSet($offset, $value) {
$this->set($offset, $value);
}
...
}
This base class allows you to get / set your object properties using the [] operator just like in Javascript:
class Boo extends Reflectable {
public $name;
}
$obj = new Boo();
$obj['name'] = "boo";
echo $obj['name']; // prints booMaybe it help anyone, if you do
<?php
$arrayAccessObject[] = 'foo';
?>
PHP give you an empty string as $offset to offsetSet($offset, $value) method.Objects implementing ArrayAccess do not support the increment/decrement operators ++ and --, unlike array() and ArrayObject()
<?php
class MyArray implements ArrayAccess
{
// offsetSet, offsetGet etc implemented
}
$x = new MyArray() ;
$x[0] = 0 ;
$x[0]++ ; //error 'Indirect modification of overloaded element has no effect'
$x[0] += 1 ; // this works OK.
?>You can use the array functions on a object of a class that implements ArrayAccess using the __invoke magic method in this way:
<?php
class ArrayVar implements ArrayAccess
{
private $data = [];
public function __invoke()
{
return $this->data;
}
}
?>
Now you can use it in this way:
<?php
$arrayar = new ArrayVar();
$arrayar['one'] = 'primer';
$arrayar['two'] = 'segon';
$arrayar['three'] = 'tercer';
$keys = array_keys($arrayar());
var_dump($keys);
// array (size=3)
// 0 => string 'one'
// 1 => string 'two'
// 2 => string 'three'
$diff = array_diff($arrayar(), [ 'two' => 'segon']);
var_dump($diff);
// array (size=2)
// 'one' => string 'primer'
// 'three' => string 'tercer'
?>