Reputation: 113
Is it possible to declare an instance of a class as a property in PHP?
Basically what I want to achieve is:
abstract class ClassA()
{
static $property = new ClassB();
}
Well, I know I can't do that, but is there any workaround beside always doing something like this:
if (!isset(ClassA::$property)) ClassA::$property = new ClassB();
Upvotes: 10
Views: 11445
Reputation: 11
This is a few years old, but I just ran into a issue where I have a base class
class GeneralObject
{
protected static $_instance;
public static function getInstance()
{
$class = get_called_class();
if(!isset(self::$_instance))
{
self::$_instance = new $class;
}
return self::$_instance;
}
}
That has a Child Class
class Master extends GeneralObject
{
}
And another Child class
class Customer extends Master
{
}
But when I try to call
$master = Master::getInstance();
$customer = Customer::getInstance();
then $master
will be Master
as expected, but $customer
will be Master
because php uses the GeneralObject::$_instance
for both Master
and Customer
The only way I could achieve what I want was to change the GeneralObject::$_instance
to be an array
and adjust the getInstance()
method.
class GeneralObject
{
protected static $_instance = array();
public static function getInstance()
{
$class = get_called_class();
if(!isset(self::$_instance[$class]))
{
self::$_instance[$class] = new $class;
}
return self::$_instance[$class];
}
}
I hope this helps someone else out there. Took me a few hours to debug what was going on.
Upvotes: 0
Reputation: 7891
you can use a singleton like implementation:
<?php
class ClassA {
private static $instance;
public static function getInstance() {
if (!isset(self::$instance)) {
self::$instance = new ClassB();
}
return self::$instance;
}
}
?>
then you can reference the instance with:
ClassA::getInstance()->someClassBMethod();
Upvotes: 22
Reputation: 1821
An alternative solution, a static constructor, is something along the lines of
<?php
abstract class ClassA {
static $property;
public static function init() {
self::$property = new ClassB();
}
} ClassA::init();
?>
Please note that the class doesn't have to be abstract for this to work.
See also How to initialize static variables and https://stackoverflow.com/a/3313137/118153.
Upvotes: 4