src/NodeTraverser.php
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 <?php
 
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 /*
  * This file is part of Twig.
  *
  * (c) Fabien Potencier
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
 
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 namespace Twig;
 
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 use Twig\NodeVisitor\NodeVisitorInterface;
 
 /**
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  * A node traverser.
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  *
  * It visits all nodes and their children and calls the given visitor for each.
  *
  * @final
  *
  * @author Fabien Potencier <fabien@symfony.com>
  */
 class NodeTraverser
 {
     protected $env;
     protected $visitors = [];
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     /**
      * @param NodeVisitorInterface[] $visitors
      */
     public function __construct(Environment $env, array $visitors = [])
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     {
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         $this->env = $env;
         foreach ($visitors as $visitor) {
             $this->addVisitor($visitor);
         }
     }
 
     public function addVisitor(NodeVisitorInterface $visitor)
     {
         $this->visitors[$visitor->getPriority()][] = $visitor;
     }
 
     /**
      * Traverses a node and calls the registered visitors.
      *
      * @return \Twig_NodeInterface
      */
     public function traverse(\Twig_NodeInterface $node)
     {
         ksort($this->visitors);
         foreach ($this->visitors as $visitors) {
             foreach ($visitors as $visitor) {
                 $node = $this->traverseForVisitor($visitor, $node);
             }
         }
 
         return $node;
     }
 
     protected function traverseForVisitor(NodeVisitorInterface $visitor, \Twig_NodeInterface $node = null)
     {
         if (null === $node) {
             return;
         }
 
         $node = $visitor->enterNode($node, $this->env);
 
         foreach ($node as $k => $n) {
             if (false !== $m = $this->traverseForVisitor($visitor, $n)) {
                 if ($m !== $n) {
                     $node->setNode($k, $m);
                 }
             } else {
                 $node->removeNode($k);
             }
         }
 
         return $visitor->leaveNode($node, $this->env);
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     }
 }
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 class_alias('Twig\NodeTraverser', 'Twig_NodeTraverser');