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Taliesin Nuin public at taliesinnuin dot net ¶
6 years ago
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");
?>
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