Array of booleans stored in a string

gistfile1.aw

<?php

/**
 * @author Arnaud Le Blanc <arnaud.lb@gmail.com>
 */
class Bitfield implements ArrayAccess
{
    protected $field;

    public function __construct($size)
    {
        $this->field = str_repeat("\xFF", ceil($size / 8));
    }

    public function offsetGet($offset)
    {
        $char = ord($this->field[$offset >> 3]);
        return (bool) ($char & (1 << ($offset & 7)));
    }

    public function offsetSet($offset, $value)
    {
        $char = ord($this->field[$offset >> 3]);
        if ($value) {
            $char |= 1 << ($offset & 7);
        } else {
            $char &= ~(1 << ($offset & 7));
        }
        $this->field[$offset >> 3] = chr($char);
    }

    public function offsetUnset($offset)
    {
        $this->offsetSet($offset, false);
    }

    public function offsetExists($offset)
    {
        return $this->offsetGet($offset);
    }
}

// bitfield with 255 booleans initialized to true
$field = new Bitfield(255);

var_dump($field[42]); // true

$field[42] = false;
var_dump($field[42]); // false

$field[42] = true;
var_dump($field[42]); // true