PHP Manual: Emit callbacks

Emit callbacks

Emit callbacks are invoked when an instance of a registered class is emitted by yaml_emit() or yaml_emit_file(). The callback is passed the object to be emitted. The callback must return an array having two keys: "tag" and "data". The value associated with the "tag" key must be a string to be used as the YAML tag in the output. The value associated with the "data" key will be encoded as YAML and emitted in place of the intercepted object.

Example #1 Emit callback example

<?php
class EmitExample {
  public $data;    // data may be in any pecl/yaml suitable type

  public function __construct ($d) {
    $this->data = $d;
  }

  /**
   * Yaml emit callback function, referred on yaml_emit call by class name.
   *
   * Expected to return an array with 2 values:
   *   - 'tag': custom tag for this serialization
   *   - 'data': value to convert to yaml (array, string, bool, number)
   *
   * @param object $obj Object to be emitted
   * @return array Tag and surrogate data to emit
   */
  public static function yamlEmit (EmitExample $obj) {
    return array(
      'tag' => '!example/emit',
      'data' => $obj->data,
    );
  }
}

$emit_callbacks = array(
  'EmitExample' => array('EmitExample', 'yamlEmit')
);

$t = new EmitExample(array('a','b','c'));
$yaml = yaml_emit(
  array(
    'example' => $t,
  ),
  YAML_ANY_ENCODING,
  YAML_ANY_BREAK,
  $emit_callbacks
);
var_dump($yaml);
?>

The above example will output something similar to:

string(43) "---
example: !example/emit
- a
- b
- c
...
"