Hey, I need help with the following Classes syntax

[elme]

I've got some classes, and each of those classes have a collection of static functions which returns an instance

of those classes, instead of having those functions in 20 different classes, I tried to move them to a parent class and inherit that class.

The problem is, when I use "return new self" from the parent class, it won't return the properties of the child it's been called from.

Here's a simple example of what i am trying to do - 

<?php

class Personal_Details{
	static function create_user(){
		return new self;
	}
}
class Female_User extends Personal_Details{
	public $gender = "f";
}

class Male_User extends Personal_Details{
	public $gender = "m";
}


$new_user = Male_User::create_user();
echo $new_user->gender;

?>

I guess I'm using the wrong logic here, but how can i make this work the way i intended to?

Thans.

[Hall of Famer]

Well you can try this:

	static function create_user(){
		return new static;
	}

The self keyword references to the very specific class in which the method is defined, in your case it is the parent class personal_detail, this is why the property $gender is undefined when you call this method. The static keyword, on the other hand, points to the very child class that calls this static method. Read this article for more details on the variation between self and static:

http://stackoverflow.com/questions/5197300/new-self-vs-new-static

 

 

Anyway incase you have to, Id recommend against calling parent's static method to create objects of its child classes, static properties/methods dont work well with inheritance and composition, they aint true OOP at all. Try rewriting the classes with instance properties/methods using factory pattern is the better idea, and its better done in a specialized factory object. 

Edited April 25, 2013 by Hall of Famer

[ignace]

class GenderEnum {
  const MALE = 'M';
  const FEMALE = 'F';
  const ALIEN = 'A';

  public static isValid($gender) {
    return in_array($gender, array(self::MALE, self::FEMALE, self::ALIEN));
  }
}

class User {
  private $gender;
  
  public function setGender($gender) {
    if (!GenderEnum::isValid($gender)) {
      throw new UnexpectedValueException();
    }
    $this->gender = $gender;
  }
}

Unless you have different behavior for your Male and Female classes these should be just one class. And by different behavior I mean:

 

class MaleUser extends User {
  public function doThingA() {
    // do stuff
  }
}

class FemaleUser extends User {
  public function doThingA() {
    // do it completely different
  }
}

[seandisanti]

If you get errors trying to implement HoF's code, check your php version as late static bindings were not available before 5.3. 

 

Id recommend against calling parent's static method to create objects of its child classes, static properties/methods dont work well with inheritance and composition, they aint true OOP at all.

 

It can be done correctly and easily, if you plan it out first. What do you mean 'aint true OOP'?  This is one function from my Model class that is extended by most of my objects that have data representations in my database. 

    public static function findById($id){
        $db = Database::getInstance();
        $sql = "SELECT * FROM " . static::$tableName . " WHERE id = " . $db->quote($id);
        return new static::$className($db->query($sql)->fetch(PDO::FETCH_ASSOC));
    }

I can then call Class::findById() from any class that extends Model, and have an instance of the object based on a row in the relevant table.

[elme]

Thank you everyone, eventually i upgraded my php to 5.4 and used "trait"