How to define a static property in PHP? - php

Question

Here is my source:
class Test {
public static function a() {
$share_var = ClassConfig::getVarA(); // return a hardcoding const 10;
// echo $share_var;
// ...
}
}
public static function b() {
$share_var = ClassConfig::getVarA(); // return a hardcoding const 10;
// echo $share_var;
// ...
}
}
}
So $share_var = ClassConfig::getVarA(); is called twice. So I do something like this:
class Test {
private static $share_var = ClassConfig::getVarA(); // return a hardcoding const 10;
public static function a() {
// echo $share_var;
// ...
}
}
public static function b() {
// echo $share_var;
// ...
}
}
}
But it failed.
How can I do that.

Answer 1

You can define the property as static, but it's no option for you because you can't call a method during class variable definition
class TestA {
private static $share_var_private = 10; // You can do this, but you can't call another method here eg TestB::a();
private static $share_var_private = Config::getA(); // This won't work
public static function a() {
echo self::$share_var_private;
}
}
If you want static methods, then you need something like own initialize method which will initialize the property but it has its disadvantages.
/**
* This is example of what I've described, but it is not so good for usage because you have to call init() method before you can use the class. You could call init method in each class method, but you can imagine it wouldn't be nice.
*/
class TestWithInit {
/**
* When it's defined as static, it can't be defined as private in php
*/
private static $share_var_static; // You can't call another class here eg TestB::a();
public static function init() {
self::$share_var_static = Config::getVarA();
}
public static function a() {
echo self::$share_var_static;
}
public static function b() {
echo self::$share_var_privat; // This would also work ... calling private variable as static (::)
}
}
Better option is probably singleton pattern which is instance of class but just once and is some ways it's quite close to static methods(NOT SAME).
class TestSingleton {
/**
* Singleton instance
*
* #var TestSingleton
*/
private $instance = null;
/**
* My special config value
*/
private $share_var;
/**
* For singleton make construct private
*/
private function __construct() {
// You can now initialize this private variable in constructor
self::$share_var = Config::getVarA();
}
/**
* Returns instance of this class
*
* #return TestSingleton
*/
public static function getInstance() {
if (self::$instance === null) {
self::$instance = new self(); // also new TestSingleton() woudl work
}
// return the instance
return self::$instance;
}
/**
* See this method is not static anymore
*/
public function a() {
echo $this->share_var_static;
}
/**
* See this method is not static anymore
*/
public function b() {
echo $this->share_var_static;
}
}
// Then you would call the method as:
TestSingleton::getInstance()->a();
TestSingleton::getInstance()->b();
// or
$myInstance = TestSingleton::getInstance();
$myInstance->a();
$myInstance->b();
Next option is to use normal non-static methods and object instance, and initialization of the object property in constructor, but I guess you know how.
I assume you wanted something more like static...

Answer 2

You must use self:
class Test {
private static $share_var = 'Something';
public static function a() {
echo self::$share_var;
}
public static function b() {
echo self::$share_var;
}
}
Test::a();
Test::b();

Answer 3

class Test {
private $share_var = ClassConfig::getVarA();
public static function a() {
echo $this->share_var;
}
public static function b() {
echo $this->share_var;
}
}
if you want to learn more about static Keyword, you can click the followed link, it's detail: static keyword