original_string: public function getCacheItem($id, $tag = null)
      {
          assert('is_string($id)');
          assert('is_null($tag) || is_string($tag)');
  
          if (!$this->isCacheValid($id, $tag)) {
              return null;
          }
  
          $cacheFile = strval($this->cacheDirectory).'/'.$id;
          return @file_get_contents($cacheFile);
      }
code: public function getCacheItem($id, $tag = null)
      {
          assert('is_string($id)');
          assert('is_null($tag) || is_string($tag)');
  
          if (!$this->isCacheValid($id, $tag)) {
              return null;
          }
  
          $cacheFile = strval($this->cacheDirectory).'/'.$id;
          return @file_get_contents($cacheFile);
      }
code_tokens: public function getCacheItem ( $ id , $ tag = null ) { assert ( 'is_string($id)' ) ; assert ( 'is_null($tag) || is_string($tag)' ) ; if ( ! $ this -> isCacheValid ( $ id , $ tag ) ) { return null ; } $ cacheFile = strval ( $ this -> cacheDirectory ) . '/' . $ id ; return @ file_get_contents ( $ cacheFile ) ; }
docstring: Get the cache item.
  
  @param string $id  The identifier of this data.
  @param string $tag  The tag that was passed to addCacheItem.
  @return string|null  The cache item, or NULL if it isn't cached or if it is expired.
docstring_tokens: Get the cache item .