Only instantiate class from within itself

Question

I am looking for a way where you can call a static method in a class, which will create an instance of itself. I would like it so it isn't possible to instantiate the class outside of itself. I have tried this, but I get an error saying Cannot instantiate abstract class (Which I assumed would happen).

abstract class Test {

    public function __construct($item){

    }

    public static function from($item){
        return new Test($item);
    }

    public function testFunc(){
        // Do some stuff
        return $this;
    }

}

It's usage would look something like this:

// Valid
Test::from($myItem)->testFunc();

// Invalid
(new Test($myItem))->testFunc();

Is there any way to do something like this?

It seems that you are trying to implement a Singleton for this class, is that it? — Jorge Campos, Feb 28 '16 at 21:52
Read about [singleton class](http://www.phptherightway.com/pages/Design-Patterns.html) design pattern — Alon Eitan, Feb 28 '16 at 21:53
See Baba's answer here: http://stackoverflow.com/questions/12553142/when-we-should-make-the-constructor-private-why-php — BenM, Feb 28 '16 at 21:54
@Marvin Ahh, that looks like it works better than the singleton.... — Get Off My Lawn, Feb 28 '16 at 21:58

score 1 · Accepted Answer · answered Feb 28 '16 at 21:58

1

You need to make the constructor private and then return the instance.. Something like this:

class Test {

    private function __construct($item){

    }

    public static function from($item){
        return new static($item);
    }

}

Now you would create new instances only like this:

$new_object = Test::from('something');

answered Feb 28 '16 at 21:58

walther

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This looks like it will do! – Get Off My Lawn Feb 28 '16 at 22:03

Only instantiate class from within itself

1 Answers1