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

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.

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.

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 ()

• If a class name is provided, the number of objects of the specified class in the object store will be returned.

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

• 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.

$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

• 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.

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 )

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:

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

• 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...

Since there were no objections against the proposed function name, its status changes to accepted.

// Proposed + Accepted
get_objects_count()

// Alternatives
get_instances_counts()
get_instances_count()
get_instance_counts()
get_object_store_count()
get_class_counts() 

No BC breaks.

next PHP 5.4.x or PHP 5.5.x

None.

None.

None.

None.

None.

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

Tests need to be done.

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

- None.

Start: 2013/04/30

End: 2013/05/07