public function getCacheFile($id)
    {
        assert('is_string($id)');

        $cacheFile = strval($this->cacheDirectory).'/'.$id;
        if (!file_exists($cacheFile)) {
            return null;
        }

        return $cacheFile;
    }
public function getCacheFile($id)
    {
        assert('is_string($id)');

        $cacheFile = strval($this->cacheDirectory).'/'.$id;
        if (!file_exists($cacheFile)) {
            return null;
        }

        return $cacheFile;
    }
public function getCacheFile ( $ id ) { assert ( 'is_string($id)' ) ; $ cacheFile = strval ( $ this -> cacheDirectory ) . '/' . $ id ; if ( ! file_exists ( $ cacheFile ) ) { return null ; } return $ cacheFile ; }
Get the cache filename for the specific id.

@param string $id  The identifier of the cached data.
@return string|null  The filename, or NULL if the cache file doesn't exist.
Get the cache filename for the specific id .