/**
* Returns $cacheKey as the cache key, so `computeCacheKey()` has
* to be called before `cache()`.
*
* @return string
*/
protected function getInputCacheKey($input)
{
if (is_file($input)) {
return $this->cacheKey;
} else {
# If $input is not a file, let the parent throw the exception.
return parent::getInputCacheKey($input);
}
}
