Question

normally using java. I ve seen a snippet like this today

$oStrategie = new Strategie();

foreach($aData as $key=>$value) {
        $oStrategie[$key] = $value;
}

$oStrategie->doSomething()

Strategie is a selfmade php class with nothing special. simple constructor doing nothing important and so on.

in the class Strategie the method doSomething() accesses the ArrayValues of $aData

$this['array_index_1'] 

Why can i access the array there even if the Strategie class doesent have any attributes defined and no setter overwritten or something like that? Can anybody explain me whats happening there? Is there no need to have attributes in the class in php???

Answer 1

Your class implements the ArrayAccess interface. This means it implements the following methods:

ArrayAccess {
    abstract public boolean offsetExists ( mixed $offset )
    abstract public mixed offsetGet ( mixed $offset )
    abstract public void offsetSet ( mixed $offset , mixed $value )
    abstract public void offsetUnset ( mixed $offset )
}

This allows you to use array access $var[$offset] on instances of this class. Here’s a standard implement of a class like this, using a $container array to hold properties:

class Strategie implements ArrayAccess {

    private $container = array();

    public function __construct() {
        $this->container = array(
            "something"   => 1,
        );
    }
    public function offsetSet($offset, $value) {
        if (is_null($offset)) {
            $this->container[] = $value;
        } else {
            $this->container[$offset] = $value;
        }
    }

    public function offsetExists($offset) {
        return isset($this->container[$offset]);
    }

    public function offsetUnset($offset) {
        unset($this->container[$offset]);
    }

    public function offsetGet($offset) {
        return isset($this->container[$offset]) ? $this->container[$offset] : null;
    }
}

Without looking at the actual implementation of Strategie or the class it’s derived from, it’s hard to tell what it’s actually doing.

But using this, you can control the behavior of the class, for example, when accessing an offset that doesn’t exist. Suppose we replace offsetGet($offset) with:

public function offsetGet($offset) {
    if (isset($this->container[$offset])) {
        return $this->container[$offset];
    } else {
        Logger.log('Tried to access: ' + $offset);
        return $this->default;
    }
}

Now whenever we try to access an offset that doesn’t exist, it will return a default (eg: $this->default) and log an error, for example.

Note that you can accomplish similar behavior using the magic methods __set(), __get(), __isset() and __unset(). The difference between the magic methods I just listed and ArrayAccess is that you’d access a property via $obj->property rather than $obj[offset]