Is it possible to create static classes in PHP (like in C#)?

I want to create a static class in PHP and have it behave like it does in C#, so

1. Constructor is automatically called on the first call to the class
2. No instantiation required

Something of this sort...

static class Hello {
    private static $greeting = 'Hello';

    private __construct() {
        $greeting .= ' There!';
    }

    public static greet(){
        echo $greeting;
    }
}

Hello::greet(); // Hello There!

Solution 1:

You can have static classes in PHP but they don't call the constructor automatically (if you try and call self::__construct() you'll get an error).

Therefore you'd have to create an initialize() function and call it in each method:

<?php

class Hello
{
    private static $greeting = 'Hello';
    private static $initialized = false;

    private static function initialize()
    {
        if (self::$initialized)
            return;

        self::$greeting .= ' There!';
        self::$initialized = true;
    }

    public static function greet()
    {
        self::initialize();
        echo self::$greeting;
    }
}

Hello::greet(); // Hello There!


?>

Solution 2:

In addition to Greg's answer, I would recommend to set the constructor private so that it is impossible to instantiate the class.

So in my humble opinion this is a more complete example based on Greg's one:

<?php

class Hello
{
    /**
     * Construct won't be called inside this class and is uncallable from
     * the outside. This prevents instantiating this class.
     * This is by purpose, because we want a static class.
     */
    private function __construct() {}
    private static $greeting = 'Hello';
    private static $initialized = false;

    private static function initialize()
    {
        if (self::$initialized)
            return;

        self::$greeting .= ' There!';
        self::$initialized = true;
    }

    public static function greet()
    {
        self::initialize();
        echo self::$greeting;
    }
}

Hello::greet(); // Hello There!


?>

Solution 3:

you can have those "static"-like classes. but i suppose, that something really important is missing: in php you don't have an app-cycle, so you won't get a real static (or singleton) in your whole application...

see Singleton in PHP

Solution 4:

final Class B{

    static $staticVar;
    static function getA(){
        self::$staticVar = New A;
    }
}

the stucture of b is calld a singeton handler you can also do it in a

Class a{
    static $instance;
    static function getA(...){
        if(!isset(self::$staticVar)){
            self::$staticVar = New A(...);
        }
        return self::$staticVar;
    }
}

this is the singleton use $a = a::getA(...);