rfc:instance_counter
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—rfc:instance_counter [2013/05/08 07:27] – [Vote] closed frank
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 +====== PHP RFC: instance counter ======
  
 +  * Version: 0.4
 +  * Date: 2013-04-08
 +  * Author: Frank Liepert, contact@frank-liepert.de
 +  * Contributor: Joe Watkins
 +  * Status: Voting
 +  * 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**
rfc/instance_counter.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1

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