What is the difference between isset() and __isset()?

Question

I need to know about magic function __isset() and normal function isset(). Actually what is the real difference between php language construct

Answer 1

in simple words, __isset() helps isset() to work over protected/private vars in class .

Example:

class test
{
    public $x = array();
}

in the above class you can do this isset($test->x['key']) as the $x is public

but here

class test
{
    protected $x = array();

    function __isset($key)
    {
        return isset($this->x[$key]);
    }
}

$x is protected and you cannot access it, so we created __isset() to help us use isset($x['key'])

you can say that __isset() is just a bridge for isset()