PHP data function to get/set data stored in private static hash.

data.php

<?php 
namespace demo;

/**
 * Get or set data.
 * @param   mixed  $key
 * @param   mixed  $val
 * @return  mixed
 */
function data($key = null, $val = null) {
    static $hash;
    $hash or $hash = array();
    $key instanceof \Closure and $key = $key($hash); # "func arg"
    $has = 1 < \func_num_args();
    if (null === $key)
        return $has ? $val : $hash; # "invalid key" or "get all"
    if (true === $key)
        return $hash = \is_array($val) ? $val : null; # reset
    if (\is_scalar($key))
        return $has ? $hash[$key] = $val : (isset($hash[$key]) ? $hash[$key] : null); # set or get
    $pre = \is_string($val) ? $val : ''; # optional prefix
    foreach ($key as $k => $v)
        $hash[$pre . $k] = $v; # set multi
    return $hash;
}