PHP : Best way to call an object method from another object ?

Question

I am searching for the best way to call a class method from another class, without having to use Global to fetch the class instance, cus as i understand now that "Global is evil" !

Here is some code to explain it more:

class Assets{
 public $assets = array();
 public function add($asset){
  $this->assets[] = $asset;
 }
}

Now i wanna call the Assets/call method from with in here ..

$assets = new Assets;
class Form{
 public function __construct(){
  global $assets;
  $assets->add('Form');
 }
}

Is using Global in such scenario is THAT bad ? If so, what other way is considered to be the best ?

PS: I need to work with only one instance of the class; means that i don't want to create a new instance inside of the second class.

Answer 1

If you only want to have 1 instance of assets, you need to use some form of dependency injection.

The most obvious in this case, is passing it through the constructor:

class Form{
 public function __construct(Assets $assets){
  $assets->add('Form');
 }
}

It is indeed a bad idea to use globals.

Answer 2

You could also make Assets a singleton if it makes sense in your context:

class Assets
{
    /////////////////////
    // Your stuff      //
    /////////////////////

    private $assets = array();
    public function add($asset)
    {
        $this->assets[] = $asset;
    }

    /////////////////////
    // Singleton stuff //
    /////////////////////

    static private $instance = null;
    static public function getInstance()
    {
        if(self::$instance == null)
            self::$instance = new self;
        return self::$instance;
    }

    // To restrict construction of this class outside of this class definition
    private function __construct() {}

    // To restrict cloning of this class outside of this class definition
    private function __clone() {}
}

In your other code, you'd use the singleton like this:

class Form
{
    public function __construct()
    {
        Assets::getInstance()->add('Form');
    }
}

Answer 3

You can try this,

class Form{
 public function __construct(Assets $assets){
  //$assets = new Assets;
  $assets->add('Form');
 }
}

Answer 4

I'm not answering this question directly with the provided elements, I just show a way of sharing data between objects without using globals.

class A {

    private $v;

    function __construct ($value)
    {
        $this->v = $value;
    }

    function set_v ($value)
    {
        $this->v = $value;
    }

    function print_v ()
    {
        echo $this->v;
    }

}

.

class B {

    private $a;

    function __construct (&$tha)
    {
        if ($tha) {
          $this->a = $tha;
        }
    }

    function print_a ()
    {
        echo $this->a->print_v();
    }
}

.

$mya = new A(12);
$mya->print_v(); // echo 12
$myb = new B($mya);
$mya->set_v(13); 
$myb->print_a(); // echo 13

You can keep a trace of one object in another and respecting the encapsulation of the objects. If an instance of A however get removed, an instance of B could get unreliable. You should then make sure that the data is always reliable within the object storing it (e.g. making a method that verify if the internal data is alright).

Also as noticed by tereško, arguments explicitly awaiting for a reference should be avoided. In fact since PHP 5.0 a new feature has been introduced to the language called the type hinting. That prevents your program to have undesired memory behavior, plus the fact that any wrong matching can be monitored at the compilation level (more details at Type Hinting (PHP official documentation))

Hence

function __construct (&$tha) ...

Must be redefined as

function __construct (A $tha) ..

in the example.

Answer 5

Dependency injection is the way to go. And i will be using this Factory mechanize to pass the object instance to the other object. As in (Just a sample, didn't test it):

class UI{

public $somthing = 'Cool';

public function newComponent($name){
    return new $name($this);
}

}

$ui = new UI;
class Form{
    public $ui;

    public function __construct(UI $ui){
        $this->ui = $ui;
    }

    public function say(){
        print $this->ui->somthing;
    }
}

$form = $ui->newComponent('Form');

$form->say(); // print 'Cool'.

Answer 6

What about

<?php
class Assets
{
    protected static $assets = array();

    protected function add($el)
    {
        self::$assets[] = $el;
    }

    public function getAssets()
    {
        return self::$assets;
    }
}

class Form extends Assets
{
    public function __construct()
    {
        parent::add('Form');
    }
}

class Css extends Assets
{
    public function __construct()
    {
        parent::add('Style');
    }
}

$assets = new Assets;
new Form;
new Css;
var_dump($assets->getAssets()); // Prints: array(2) { [0]=> string(4) "Form" [1]=> string(5) "Style" }