PHP OOP - How do I define a CONST with a Variable or Function Output?

Question

My specific case is that I am trying to define a path into a constant. Right now I hard code as such:

class Cache
{
   const PATH_TO_CACHE = '/home/site/public_html/wp-content/themes/theme/cache/';

But I need the define to be portable. So the path can be detected, put in a variable, then put in the class. Essentially, what I want to accomplish is:

$somepath = {code to get path};

class Cache 
{
const PATH_TO_CACHE = $somepath;

Answer 1

I like to use dependency injection for this. For example:

class Cache {

  private $path_to_cache;

  function __construct($cache_path) {
    $this->path_to_cache = $cache_path;
  } 

}

Then you can use a defined setting:

$cache = new Cache($GLOBALS['config']['cache_path']);
$cache = new Cache($_SERVER['cache_path']);
$cache = new Cache($some_other_way_to_get_cache_path);

etc.

You can also easily change the path when developing / debugging:

$cache = new Cache('path/to/folder/that/is/being/problematic');

Answer 2

Actually there is a workaround for this:

class Cache 
{
    const PATH_TO_CACHE = 'whateverYouWantToNameIt';

    private $_config = array(
        self::PATH_TO_CACHE => ''
    );

    public __construct() {
        $somePath = 'construct this path by your rules';
        $this->_config[self::PATH_TO_CACHE] = $somepath;
    }

    public function getConfig($configKey)
    {
        if (array_key_exists($configKey, $this->_config)) {
            return $this->_config[$configKey];
        }
    }
}

Basically you create an array with a key as a constant and this way you can always get that value like so:

$cacheObj = new Cache();
$somePath = $cacheObj->getConfig(Cache::PATH_TO_CACHE);

My guess is that you intend to force the users of the class to access that path via a constant value. However this method shouldn't be used if you only have one constant, it beats the purpose of an array.