How to implements _isset magic method?

Question

I try to implement the __isset magic method such as the following code,

Why do I always get an undefined index error? can anyone tell me how to do?

class c {
    public $x = array();
    public function __get($name) {
        return $this->x[$name]; //undefined index: #1:a / #2:b / #3:d
    }
    public function __isset($name) {
        return isset($this->x[$name]);
    }
}

$c = new c;
var_dump(isset($c->a));      
var_dump(isset($c->a->b));   #1
var_dump(isset($c->b->c));   #2
var_dump(isset($c->d['e'])); #3

Why the following code is working fine? I don't understand?

$x = array();
var_dump(isset($x->a->b->c));       
var_dump(isset($x['a']['b']['c']));

Answer 1

You might expect, that the PHP engine will call __isset() before every access to hidden properties in PHP. But thats not true. Check the documentation:

__isset() is triggered by calling isset() or empty() on inaccessible properties.

So, that's expected behaviour, as only:

var_dump(isset($c->a));

will trigger __isset().

All of the other lines will just trigger __get(). And as you didn't set those indexes it is expected behaviour.

Change your code to:

class c {
    public $x = array();
    public function __get($name) {
        var_dump(__METHOD__);
        return $this->x[$name];
    }
    public function __isset($name) {
        var_dump(__METHOD__);
        return isset($this->x[$name]);
    }
}

to see which methods are actually called. This will give you:

c::__isset   <------ called!
bool(false)
c::__get

Notice: Undefined index: a in /tmp/a.php on line 6

Call Stack:
    0.0002     647216   1. {main}() /tmp/a.php:0
    0.0003     648472   2. c->__get() /tmp/a.php:16

<---------------------- not called 
bool(false)
c::__get

Notice: Undefined index: b in /tmp/a.php on line 6

Call Stack:
    0.0002     647216   1. {main}() /tmp/a.php:0
    0.0005     648656   2. c->__get() /tmp/a.php:17

<---------------------- not called     
bool(false)
c::__get

Notice: Undefined index: d in /tmp/a.php on line 6

Call Stack:
    0.0002     647216   1. {main}() /tmp/a.php:0
    0.0006     648840   2. c->__get() /tmp/a.php:18

<---------------------- not called     
bool(false)