PHP: rfc:instance_counter

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== PHP RFC: instance counter ======

  * Version: 0.4
  * Date: 2013-04-08
  * Author: Frank Liepert, contact@frank-liepert.de
  * Contributor: Joe Watkins
  * Status: Declined
  * First Published at: http://wiki.php.net/rfc/instance_counter

===== Introduction =====

Coming to Object-Orientated Programming, PHP offers a variety of possibilities to obtain information about classes and their instances (objects). In this regard, the classes/objects functions (http://www.php.net/manual/en/ref.classobj.php) as well as the reflection API (http://www.php.net/manual/en/book.reflection.php) do a great job. But still there is no function to obtain a particular information: the number of instances of a class. 

One might say, simply implement a static counter in each class. But what about built-in classes like SPL? A wrapper would be required. Implementing it these ways, it not only sounds, but actually is cumbersome. The purpose of this RFC is to address this issue.

===== Proposal =====

The proposal is to add a new functionality dealing with the number of instances of either a specific class name/object or set of class names/objects or all classes.

The function name should fit in with the current names of class/object functions. Therefore, the name **get_objects_count()** seems to be reasonable.

  * **If no argument is provided, the number of all objects in the object store as an associative array ('class name' => count) will be returned.**
<code php>
print_r (get_objects_count());
// Array ()

$foo = new stdClass;

print_r (get_objects_count());
// Array ( [stdClass] => 1 )

$bar = new stdClass;

print_r (get_objects_count());
// Array ( [stdClass] => 2 )

$bar = null;

print_r (get_objects_count());
// Array ( [stdClass] => 1 )

$foo = null;

print_r (get_objects_count());
// Array ()
</code>

  * **If a class name is provided, the number of objects of the specified class in the object store will be returned.**
<code php>
print get_objects_count('stdClass');
// 0

$foo = new stdClass;

print get_objects_count('stdClass');
// 1

$bar = new stdClass;

print get_objects_count('stdClass');
// 2

$bar = null;

print get_objects_count('stdClass');
// 1

$foo = null;

print get_objects_count('stdClass');
// 0
</code>

  * **If an object is provided, the number of objects of the specifiied objects class in the object store will be returned. The return value is always ≥ 1.**
<code php>
$foo = new stdClass;

print get_objects_count($foo);
// 1

$bar = new stdClass;

print get_objects_count($bar);
// 2

$bar = null;

print get_objects_count($foo);
// 1
</code>

  * **If an an array is provided, it will be the treated as an inclusive indexed array of class names. An associative array ('class name' => count) will be returned.**
<code php>
print_r (get_objects_count(array('stdClass')));
// Array ( [stdClass] => 0 )

$foo = new stdClass;

print_r (get_objects_count(array('stdClass')));
// Array ( [stdClass] => 1 )

$bar = new stdClass;

print_r (get_objects_count(array('stdClass')));
// Array ( [stdClass] => 2 )

$bar = null;

print_r (get_objects_count(array('stdClass')));
// Array ( [stdClass] => 1 )

$foo = null;

print_r (get_objects_count(array('stdClass')));
// Array ( [stdClass] => 0 )
</code>

===== General questions & answers =====

==== Inheritance ====

On internals list there was the question, if only the "direct" instances of a class or also the instances of subclasses are counted? The answer is: only direct instances. See the following code:
<code php>
class A {}
class B extends A {}

print get_objects_count('A');
// 0

$b = new B;

var_dump($b instanceof A);
// bool(true)

print get_objects_count('A');
// 0

print get_objects_count('B');
// 1
</code>

===== Use cases: =====
  * Debugging
  * Implementation of design patterns (f.ex. flyweight pattern)
  * Extended control: limit the number of objects
  * Teach people about assignment of objects
  * to be continued...

===== Function name =====

Since there were no objections against the proposed function name, its status changes to accepted.
<code>
// Proposed + Accepted
get_objects_count()

// Alternatives
get_instances_counts()
get_instances_count()
get_instance_counts()
get_object_store_count()
get_class_counts() 
</code>

===== Backward Incompatible Changes =====

No BC breaks.

===== Proposed PHP Version(s) =====

next PHP 5.4.x or PHP 5.5.x

===== SAPIs Impacted =====

None.

===== Impact to Existing Extensions =====

None.

===== New Constants =====

None.

===== php.ini Defaults =====

None.

===== Open Issues =====

None.
===== Patches and Tests =====

Implementation: https://gist.github.com/krakjoe/5275773

Tests need to be done.

===== References =====

  * https://gist.github.com/krakjoe/5275773
  * http://www.php.net/manual/en/ref.classobj.php
  * http://www.php.net/manual/en/book.reflection.php

===== Rejected Features =====

- None.

===== Vote =====
<doodle title="Should this RFC be implemented?" auth="frank" voteType="single" closed="true">
   * Yes
   * No
</doodle>
    
==== Voting period ====
Start: **2013/04/30**

End: **2013/05/07**
Page Tools
