Question

Consider the following code:

class Vehicle {

    /**
    * Create a new instance of Vehicle
    * 
    * @return Vehicle
    */
    public static function create(){

        return eval( "return new " . get_called_class() . '();' );
        // return self(); would always return Vehicle reg ardless

    }


    public function drive(){

        echo "I am a Vehicle!";

    }

}

class Bus extends Vehicle {

    public function drive(){

        parent::drive();

        echo "\nSpecifically, a bus!";

    }

}


class Car extends Vehicle {

    public function drive(){

        parent::drive();

        echo "\nSpecifically, a car!";

    }

}

// Drive a car
    Car::create()->drive();

// Drive a bus
    Bus::create()->drive();

I’ve implemented a factory “create” method in the Vehicle class that allows me to get an instance of the class that I want to use.

I tried using “return new self();” but that always returns an instance of Vehicle, so I resorted to using eval.

question: Is there a non-eval way to implement the create() method so that:

• it returns an instance of the class you’re using
• it doesn’t require implementing create() on each of the extending classes

Answer 1

Use static instead of self, e.g.

<?php
class Vehicle {
    public static function create(){
        return new static();
    }

    public function drive(){
        echo "I am a Vehicle!";
    }
}

class Bus extends Vehicle {
    public function drive(){
        parent::drive();
        echo "\nSpecifically, a bus!";

    }
}

$b = Bus::create();
$b->drive();

prints

I am a Vehicle!
Specifically, a bus!