A little PHP trick

How to realize that when a time-consuming function or class method is called multiple times, the operation is performed for the first time, and the result is returned directly when the function is called again?

<?php 

class MyDate
{
    public static function getCurrentDate()
    {
        static $current_date = &#39;&#39;;

        if (!$current_date) {
            echo &#39;only run one time&#39;;
            usleep(200000);
            $current_date  = date(&#39;Y-m-d H:i:s&#39;);
        }

        return $current_date;
    }

    public static function getCurrentDate2()
    {
        usleep(200000);
        echo &#39;run everytime&#39;;
        return date(&#39;Y-m-d H:i:s&#39;);
    }
}

$start = microtime(true);
$i = 5;
while ($i--) {
    MyDate::getCurrentDate();
}
echo microtime(true) - $start;    //200ms

$start = microtime(true);
$i = 5;
while ($i--) {
    MyDate::getCurrentDate2();
}
echo microtime(true) - $start;    //1s