I came across a problem having developed a site with a PHP 5.3 environment, when moving the site to the live environment the server was running PHP 5.2. Whilst the server gets upgraded I looked into getting the code to work in some form in the meantime. The main issues are the functions lcfirst() and date_diff(). The former is a simple fix, a function which lower-cases the first letter of a string — I was surprised this was only introduced in 5.3!

if(function_exists('lcfirst') === false) {
  function lcfirst($str) {
    $str[0] = strtolower($str[0]);
    return $str;
  }
}

The issue with date_diff is it’s reliance on the DateInterval class, which as the name suggests is a native object introduced in 5.3 to represent the interval between two dates. The function ought to be functionally equivalent between both PHP 5.2 and 5.3, otherwise it would be useless. I found something that I am fairly happy with, in that it accepts the same inputs and outputs as the native 5.3 version. The calculations aren’t correct though, unfortunately, and it’s an incomplete implementation. I corrected the “invert” data type values returned, and also added support for “days” as these are the main things I am using.

/**
* Workaround for PHP < 5.3.0
*/
if(!function_exists('date_diff')) {
  class DateInterval {
    public $y;
    public $m;
    public $d;
    public $h;
    public $i;
    public $s;
    public $invert;
    public $days;
 
    public function format($format) {
      $format = str_replace('%R%y', 
        ($this->invert ? '-' : '+') . $this->y, $format);
      $format = str_replace('%R%m', 
         ($this->invert ? '-' : '+') . $this->m, $format);
      $format = str_replace('%R%d', 
         ($this->invert ? '-' : '+') . $this->d, $format);
      $format = str_replace('%R%h', 
         ($this->invert ? '-' : '+') . $this->h, $format);
      $format = str_replace('%R%i', 
         ($this->invert ? '-' : '+') . $this->i, $format);
      $format = str_replace('%R%s', 
         ($this->invert ? '-' : '+') . $this->s, $format);
 
      $format = str_replace('%y', $this->y, $format);
      $format = str_replace('%m', $this->m, $format);
      $format = str_replace('%d', $this->d, $format);
      $format = str_replace('%h', $this->h, $format);
      $format = str_replace('%i', $this->i, $format);
      $format = str_replace('%s', $this->s, $format);
 
      return $format;
    }
  }
 
  function date_diff(DateTime $date1, DateTime $date2) {
 
    $diff = new DateInterval();
 
    if($date1 > $date2) {
      $tmp = $date1;
      $date1 = $date2;
      $date2 = $tmp;
      $diff->invert = 1;
    } else {
      $diff->invert = 0;
    }
 
    $diff->y = ((int) $date2->format('Y')) - ((int) $date1->format('Y'));
    $diff->m = ((int) $date2->format('n')) - ((int) $date1->format('n'));
    if($diff->m < 0) {
      $diff->y -= 1;
      $diff->m = $diff->m + 12;
    }
    $diff->d = ((int) $date2->format('j')) - ((int) $date1->format('j'));
    if($diff->d < 0) {
      $diff->m -= 1;
      $diff->d = $diff->d + ((int) $date1->format('t'));
    }
    $diff->h = ((int) $date2->format('G')) - ((int) $date1->format('G'));
    if($diff->h < 0) {
      $diff->d -= 1;
      $diff->h = $diff->h + 24;
    }
    $diff->i = ((int) $date2->format('i')) - ((int) $date1->format('i'));
    if($diff->i < 0) {
      $diff->h -= 1;
      $diff->i = $diff->i + 60;
    }
    $diff->s = ((int) $date2->format('s')) - ((int) $date1->format('s'));
    if($diff->s < 0) {
      $diff->i -= 1;
      $diff->s = $diff->s + 60;
    }
 
    $start_ts   = $date1->format('U');
    $end_ts   = $date2->format('U');
    $days     = $end_ts - $start_ts;
    $diff->days  = round($days / 86400);
 
    if (($diff->h > 0 || $diff->i > 0 || $diff->s > 0))
      $diff->days += ((bool) $diff->invert)
        ? 1
        : -1;
 
    return $diff;
 
  }
 
}

It works pretty well (bar the inaccuracies), and hopefully I won’t have a use for it again anyway.