Can I freely set members in php? - php

Question

Can I freely assign something to non-existent or not-known-existent members in php? Is there any difference between member names and associative array index?
I there any difference beteween
$a = array();
$a['foo'] = 'something';
and
$a->foo = 'something';
If there is a difference, then how can I create "empty" object and add members dynamically to it?

Answer 1

You are mixing Arrays (which are bags/containers for data) and Objects (which are wrappings for data with semantic meaning and functionality).
Array Access
The first is correct since you are using an Array which acts like a HashTable or Dictionary in other languages.
$a = array(); // create an empty "box"
$a['foo'] = 'something'; // add something to this array
Object Access
The second is an Object access. You would use something like this:
class Foo {
public $foo;
}
$a = new Foo();
$a->foo = 'something';
Although the better usage in that case is to use a setter/getter approach like this.
class Foo {
private $foo;
public function setFoo($value) {
$this->foo = $value;
}
public function getFoo() {
return $this->foo;
}
}
$a = new Foo();
$a->setFoo('something');
var_dump($a->getFoo());
PHP Magic
However there is still an option to use PHPs Magic Methods to create a behavior like you describe it. Nevertheless this should be considers not the usual way of storing data to a object since this lead to errors and gives you a much harder time with (unit) testing.
class Foo {
private $data = array();
public function __set($key, $value) {
$this->data[$key] = $value;
}
public function __get($key) {
return $this->data[$key];
}
}
$a = new Foo();
$a->foo = 'something'; // this will call the magic __set() method
var_dump($a->foo) // this will call the magic __get() method
This hopefully did help you solving your problem.

Answer 2

If you want to assign arbitrary members to an object as you do on an associative array, you'll probably want to look into PHP's magic property overloading.
Here's an example class that will let you just assign and retrieve variables (mostly taken from the PHP documentation):
<?php
class PropertyTest
{
/** Location for overloaded data. */
private $data = array();
public function __set($key, $value) {
$this->data[$key] = $value;
}
public function __get($key) {
return $this->data[$key];
}
}
// sample use:
$a = new PropertyTest();
$a->foo = "bar";
echo $a->foo; // will print "bar"
?>

Answer 3

You can create an empty class object and afterwards add properties to it, e.g.:
<?php
$myObject = new StdClass();
$myObject->id = 1;
$myObject->name = "Franky";
$myObject->url = "http://www.google.com";
var_dump($myObject);
...this should produce
object(stdClass)#1 (3) { ["id"]=> int(1) ["name"]=> string(6) "Franky" ["url"]=> string(21) "http://www.google.com" }
Personally, I prefer using object classes instead of arrays.