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WordPress

Walker::walk( array $elements, int $max_depth, mixed $args ): string

Since
2.1.0, 5.3.0
Source
wp-includes/class-wp-walker.php:194
Displays array of elements hierarchically.

Description

Does not assume any existing order of elements.

$max_depth = -1 means flatly display every element.
$max_depth = 0 means display all levels.
$max_depth > 0 specifies the number of display levels.

Compatibility

WordPress
since 5.3.0
PHP
7.4–8.6-dev
  • 6.7.7
  • 6.8.8
  • 6.9.7
  • 7.0.4
  • 7.1.0

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$elementsarray
An array of elements.
$max_depthint
The maximum hierarchical depth.
$argsmixed
Optional additional arguments.

Return value

string
The hierarchical item output.

Performance profile

How much work a call to Walker::walk() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class
Light

Touches nothing outside its own arguments.

Scaling
Scales with input

The body loops, so the work grows with what you pass in.

Instructions
9–46

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 105.

Plugin surface
None

Nothing here hands control to plugin code.

Called by
0

Nothing in core calls this; the cost is only what you spend yourself.

What one call costs · 2 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost Walker::walk() can have, taken from its control-flow graph on PHP 8.5.

WhenInstructionsCalls it makes
always9–34none
!$max_depth && !empty($elements) && $max_depth !== -1 && empty($top_level_elements)36–46array_slice()

Across PHP versions

Compiles the same on PHP 7.4, 8.1, 8.2, 8.3, 8.4, 8.5 and 8.6-dev: 105 instructions, 9–46 executed per call, 20 branches. The work does not change between versions.

An instruction is not a fixed amount of time, so a matching count is not necessarily the same speed; what it rules out is a difference in the work itself.

Uses · 1

Source code

View on Trac View on GitHub 

	public function walk( $elements, $max_depth, ...$args ) {		$output = ''; 		$max_depth = (int) $max_depth; 		// Invalid parameter or nothing to walk.		if ( $max_depth < -1 || empty( $elements ) ) {			return $output;		} 		$parent_field = $this->db_fields['parent']; 		// Flat display.		if ( -1 === $max_depth ) {			$empty_array = array();			foreach ( $elements as $e ) {				$this->display_element( $e, $empty_array, 1, 0, $args, $output );			}			return $output;		} 		/*		 * Need to display in hierarchical order.		 * Separate elements into two buckets: top level and children elements.		 * Children_elements is two dimensional array. Example:		 * Children_elements[10][] contains all sub-elements whose parent is 10.		 */		$top_level_elements = array();		$children_elements  = array();		foreach ( $elements as $e ) {			if ( empty( $e->$parent_field ) ) {				$top_level_elements[] = $e;			} else {				$children_elements[ $e->$parent_field ][] = $e;			}		} 		/*		 * When none of the elements is top level.		 * Assume the first one must be root of the sub elements.		 */		if ( empty( $top_level_elements ) ) { 			$first = array_slice( $elements, 0, 1 );			$root  = $first[0]; 			$top_level_elements = array();			$children_elements  = array();			foreach ( $elements as $e ) {				if ( $root->$parent_field === $e->$parent_field ) {					$top_level_elements[] = $e;				} else {					$children_elements[ $e->$parent_field ][] = $e;				}			}		} 		foreach ( $top_level_elements as $e ) {			$this->display_element( $e, $children_elements, $max_depth, 0, $args, $output );		} 		/*		 * If we are displaying all levels, and remaining children_elements is not empty,		 * then we got orphans, which should be displayed regardless.		 */		if ( ( 0 === $max_depth ) && count( $children_elements ) > 0 ) {			$empty_array = array();			foreach ( $children_elements as $orphans ) {				foreach ( $orphans as $op ) {					$this->display_element( $op, $empty_array, 1, 0, $args, $output );				}			}		} 		return $output;	}

Changelog

Introduced in 2.1.0. Unchanged from 6.7.7 through 7.1.0.

  1. 6.7.7
  2. 6.8.8
  3. 6.9.7
  4. 7.0.4
  5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

5.3.0
Formalized the existing ...$args parameter by adding it to the function signature.from the docblock
2.1.0
Introduced.from the docblock

About this page

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Generated from the wordpress-develop 6.9.7 tag, from src/wp-includes/class-wp-walker.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.
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