FAQ.markdown

Frequently Asked Questions

• How can the parent of a node be obtained?
• How can the next/previous 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:

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:

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').