code: public function getCacheDirectory()
      {
          if (!is_null($this->cacheDirectory)) {
              return $this->cacheDirectory;
          }
          if (defined('PHP_WINDOWS_VERSION_MAJOR')) {
              if (!getenv('APPDATA')) {
                  throw new RuntimeException(
                      'The APPDATA environment variable must be set for humbug.'
                  );
              }
              $home = strtr(getenv('APPDATA'), '\\', '/') . '/Humbug';
          } else {
              if (!getenv('HOME')) {
                  throw new RuntimeException(
                      'The HOME environment variable must be set for humbug.'
                  );
              }
              $home = rtrim(getenv('HOME'), '/') . '/.humbug';
          }
          $cache = $home . '/cache';
          foreach ([$home, $cache] as $dir) {
              if (!is_dir($dir)) {
                  mkdir($dir, 0777);
              }
          }
          file_put_contents($home . '/.htaccess', 'Deny from all');
          $this->cacheDirectory = $cache;
          return $cache;
      }
docs: Get the cache directory.
  
  @return string