Object Iteration

Question

I know that iteration over an object is equal to iterating over the visible properties of the class.

class MyClass
{
    public $var1 = 'value 1';
    public $var2 = 'value 2';
    public $var3 = 'value 3';

    protected $protected = 'protected var';
    private   $private   = 'private var';
}

$class = new MyClass();

foreach($class as $key => $value) {
    print "$key => $value\n"; // print all visible attributes
}

I'm curious to know why iteration over an object that doesn't implement any interface causes iteration over its visible variables? And what is the use case of this ability?

What feature are you talking about specifically? It doesn't seem clear from your question. — Script47, Mar 06 '19 at 09:01
@Script47I mean why iterate over an object that doesn't implement any interface cause iterate over its visible variables — hoseinz3, Mar 06 '19 at 09:06
Do you mean *Why* because "Why have this ability?" or *Why* because "Why does this work this way?" — Martin, Mar 06 '19 at 09:09
What do you mean by "use case"? If you have none, that's fine. There are tons of features in PHP that I've never used, but I would not question that there is anybody else out there who has — Nico Haase, Mar 06 '19 at 09:13
@Martin I mean why have this ability? or is there any use case that people use to iterate over the object to iterate through its visible properties? — hoseinz3, Mar 06 '19 at 09:17
Object is a collection of properties and methods. Built-in control structure `foreach` allows you to iterate over the array items, and visible properties in object and that is built in feature. This is related with your question https://stackoverflow.com/questions/10057671/how-does-php-foreach-actually-work — Nikola Kirincic, Mar 06 '19 at 09:22

score 3 · Accepted Answer · answered Mar 06 '19 at 09:10

As far as you have declared class structure it's usually useless or at least a bad practice.

But PHP also allows you to dynamically create properties on objects, so its structure isn't implied by class definition.

You could do:

$class = new MyClass();
$class->nonExistingProperty = 123;

And then iteration over this object would return nonExistingProperty too.

That is a bad practice, but it is possible. It is sometimes used on containers for view data (Zend 1 as far as I remember).

Also there's a predefined stdClass which is designed to create "dynamic objects". For example it's used by json_decode() function.

So for example in case of decoding JSON document you may want to iterate over its properties without knowledge about its structure (it might be dynamic too).

Object Iteration

1 Answers1