static $init; 
if (!isset($init)) 
{ // We never want to unserialize !php/object. 
ini_set('yaml.decode_php', 0); 
$init = TRUE; 
} 

$data = yaml_parse($raw, 0, $ndocs, [ 
YAML_BOOL_TAG => '\Drupal\Component\Serialization\YamlPecl::applyBooleanCallbacks', ]); 

yamlparse
(PECL yaml >= 0.4.0) yaml_parse — Parse a YAML stream
Description 
mixed yaml_parse ( string $input [, int $pos = 0 [, int &$ndocs [, array $callbacks = null ]]] ) Convert all or part of a YAML document stream to a PHP variable.
Parameters 
input The string to parse as a YAML document stream.
pos Document to extract from stream (-1 for all documents, 0 for first document, ...).
ndocs If ndocs is provided, then it is filled with the number of documents found in stream.
callbacks Content handlers for YAML nodes. Associative array of YAML tag => callable mappings. See parse callbacks for more details.
Return Values 
Returns the value encoded in input in appropriate PHP type or FALSE on failure. If pos is -1 an array will be returned with one entry for each document found in the stream.    

 Notes 
Warning Processing untrusted user input with yamlparse() is dangerous if the use of unserialize() is enabled for nodes using the !php/object tag. This behavior can be disabled by using the yaml.decodephp ini setting. 

 public static function decode($raw) {
$serializer = static::getSerializer(); 
return $serializer::decode($raw); 
}

protected static function getSerializer() {
if (!isset(static::$serializer)) {
  // Use the PECL YAML extension if it is available. It has better
  // performance for file reads and is YAML compliant.
  if (extension_loaded('yaml')) {
    static::$serializer = YamlPecl::class;
  }
  else {
    // Otherwise, fallback to the Symfony implementation.
    static::$serializer = YamlSymfony::class;
  }
}
return static::$serializer;
} 

public function validateForm(array &$form, FormStateInterface $form_state) { // The confirmation step needs no additional validation. if ($this->data) { return; }
try {
  // Decode the submitted import.
  $data = Yaml::decode($form_state->getValue('import'));
}
catch (InvalidDataTypeException $e) {
  $form_state->setErrorByName('import', $this->t('The import failed with the following message: %message', ['%message' => $e->getMessage()]));
}

public function __destruct()
 { 
$this->close(); $this->removeFiles(); 
}
 private function removeFiles() 
{ 
foreach ($this->files as $filename) 
{ if (file_exists($filename)) { @unlink($filename); } } 
$this->files = array();
}

public function __destruct() { $this->save($this->filename); }
/**
Saves the cookies to a file. *
@param string $filename File to save
@throws \RuntimeException if the file cannot be found or created */ 
public function save($filename) { 
$json = []; 
foreach ($this as $cookie) { /* @var SetCookie $cookie */ 
if (CookieJar::shouldPersist($cookie, $this->storeSessionCookies)) { 
$json[] = $cookie->toArray(); 
} 
}
$jsonStr = \GuzzleHttp\jsonencode($json); 
if (false === fileput_contents($filename, $jsonStr)) 
{ throw new \RuntimeException("Unable to save file {$filename}"); } 
} 

public function __destruct() { 
if (isset($this->_fn_close)) { call_user_func($this->_fn_close); } 
} 

  public static function decode($raw) {
    static $init;
    if (!isset($init)) {
      // We never want to unserialize !php/object.
      ini_set('yaml.decode_php', 0);
      $init = TRUE;
    }
    // yaml_parse() will error with an empty value.
    if (!trim($raw)) {
      return NULL;
    }
......
}