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Frequently Asked Questions
==========================
* [How can the parent of a node be obtained?](#how-can-the-parent-of-a-node-be-obtained)
* [How can the next/previous sibling of a node be obtained?](#how-can-the-nextprevious-sibling-of-a-node-be-obtained)
How can the parent of a node be obtained?
-----
The AST does not store parent nodes by default. However, the `ParentConnectingVisitor` can be used to achieve this:
```php
use PhpParser\NodeTraverser;
use PhpParser\NodeVisitor\ParentConnectingVisitor;
use PhpParser\ParserFactory;
$code = '...';
$traverser = new NodeTraverser(new ParentConnectingVisitor);
$parser = (new ParserFactory())->createForHostVersion();
$ast = $parser->parse($code);
$ast = $traverser->traverse($ast);
```
After running this visitor, the parent node can be obtained through `$node->getAttribute('parent')`.
How can the next/previous sibling of a node be obtained?
-----
Again, siblings are not stored by default, but the `NodeConnectingVisitor` can be used to store
the previous / next node with a common parent as well:
```php
use PhpParser\NodeTraverser;
use PhpParser\NodeVisitor\NodeConnectingVisitor;
use PhpParser\ParserFactory;
$code = '...';
$traverser = new NodeTraverser(new NodeConnectingVisitor);
$parser = (new ParserFactory())->createForHostVersion();
$ast = $parser->parse($code);
$ast = $traverser->traverse($ast);
```
After running this visitor, the parent node can be obtained through `$node->getAttribute('parent')`,
the previous node can be obtained through `$node->getAttribute('previous')`, and the next node can be
obtained through `$node->getAttribute('next')`.
`ParentConnectingVisitor` and `NodeConnectingVisitor` should not be used at the same time. The latter
includes the functionality of the former.
How can I limit the impact of cyclic references in the AST?
-----
NodeConnectingVisitor adds a parent reference, which introduces a cycle. This means that the AST can now only be collected by the cycle garbage collector.
This in turn can lead to performance and/or memory issues.
To break the cyclic references between AST nodes `NodeConnectingVisitor` supports a boolean `$weakReferences` constructor parameter.
When set to `true`, all attributes added by `NodeConnectingVisitor` will be wrapped into a `WeakReference` object.
After enabling this parameter, the parent node can be obtained through `$node->getAttribute('weak_parent')`,
the previous node can be obtained through `$node->getAttribute('weak_previous')`, and the next node can be
obtained through `$node->getAttribute('weak_next')`.
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