PHP RFC: __debugInfo()

PHP RFC: __debugInfo()

Version: 1.1
Date: 2014-01-21
Author: Sara Golemon, pollita@php.net
Status: Accepted (implemented in 5.6)
First Published at: http://wiki.php.net/rfc/debug-info

Proposal

This RFC is for exposing the “get_debug_info” API already available to internal classes (written in C) to PHP classes via a magic method called __debugInfo().

Example Usage:

class File {
  // "Resource(stream)" isn't all that useful
  private $fp;

  // But all the stream meta data is
  public function __debugInfo() {
    return $this->fp ? stream_get_meta_data($fp) : [];
  }

  public function open($filename, $mode = 'r'){
    $this->fp = fopen($filename, $mode);
  }  
}

$f = new File;
var_dump($f); // object(File)#1 { }
$f->open('http://php.net');
var_dump($f);
/*
object(File)#1 {
  ["wrapper_type"]=>
  string(4) "http"
  ["stream_type"]=>
  string(10) "tcp_socket"
  etc...
*/

Backward Incompatible Changes

Double underscore is a reserved namespace, so any classes which happen to implement this are the ones which need to change.

Impact to Existing Extensions

Existing fallback behavior for internal classes not overriding get_debug_info is preserved via chaining to get_properties when no __debugInfo function is defined.

Proposed PHP Version(s)

5.next

Alternates under discussion

Rather than use __debugInfo() as the whole property info result, either merge it with the properties table or stuff it into a "__debugInfo" property and return it with the full properties table.

IMO, this takes control away from the user and removes a particularly useful reason for having the __debugInfo() magic method in the first place. Consider an object which points at itself (or more likely, another object which points back at the original). This normally results in a recursive loop. This is detected by the var_dump() routine, but only after a couple cycles. A more intelligent __debugInfo() output could avoid any iterations of the loop.