Demonstrates how to have a static cache variable (array) which is capped to a maximum count of entries, with last-in-first-out.

cappedStaticCacheVAR.php

<?php
/**
 * Demonstrate how to have a static cache variable that is capped to a maximum count.
 *
 * User: sarel
 * Date: 2014/03/06
 * Time: 8:27 PM
 */

class testShifting {
    public static $cache = array();

    const CACHE_MAX = 5;

    public function calculateSomething () {

        if (count(self::$cache) >= self::CACHE_MAX) {
            array_shift(self::$cache);
        }

        self::$cache[] = date('Y-m-d H:i:s');
    }
}

$bleh = new testShifting();

for ($i = 0; $i < 7; $i++) {
    $bleh->calculateSomething();
    print_r(testShifting::$cache);
    sleep(1);
}

The cap is 5, so we only always want 5 entries in the array, this will thus yield:

Array
(
    [0] => 2014-03-06 20:35:57
)
Array
(
    [0] => 2014-03-06 20:35:57
    [1] => 2014-03-06 20:35:58
)
Array
(
    [0] => 2014-03-06 20:35:57
    [1] => 2014-03-06 20:35:58
    [2] => 2014-03-06 20:35:59
)
Array
(
    [0] => 2014-03-06 20:35:57
    [1] => 2014-03-06 20:35:58
    [2] => 2014-03-06 20:35:59
    [3] => 2014-03-06 20:36:00
)
Array
(
    [0] => 2014-03-06 20:35:57
    [1] => 2014-03-06 20:35:58
    [2] => 2014-03-06 20:35:59
    [3] => 2014-03-06 20:36:00
    [4] => 2014-03-06 20:36:01
)
Array
(
    [0] => 2014-03-06 20:35:58
    [1] => 2014-03-06 20:35:59
    [2] => 2014-03-06 20:36:00
    [3] => 2014-03-06 20:36:01
    [4] => 2014-03-06 20:36:02
)
Array
(
    [0] => 2014-03-06 20:35:59
    [1] => 2014-03-06 20:36:00
    [2] => 2014-03-06 20:36:01
    [3] => 2014-03-06 20:36:02
    [4] => 2014-03-06 20:36:03
)