Question

Example php code:

class TestArrayObject extends ArrayObject {
    function offsetSet($index,$val){
        echo $index.':'.$val.PHP_EOL;
    }
}

$s = new TestArrayObject();

//test 1
$s['a'] = 'value';//calls offsetSet
//test 2
$s['b']['c'] = 'value';//does not call offsetSet, why?

var_dump($s);

why doesn’t test 2 call the offsetSet method?

Answer 1

ArrayObject is a big chunk of magic and thus I wouldn’t recommend using it or – even worse – extending it.

But your actual problem hasn’t to do with ArrayObject by itself. What you are running into is that $s['b']['c'] = ...; is a so called indirect modification of the 'b' offset. The code that PHP executes for it looks roughly like this:

$offset =& $s['b'];
$offset['c'] = ...;

As you can see offset 'b' is never directly written to. Instead it is fetched by reference and the reference is modified. That’s why offsetGet will be called, not offsetSet.