PHP Classes: when to use :: vs. ->?

Question

I understand that there are two ways to access a PHP class - \"::\" and \"->\". Sometime one seems to work for me, while the other doesn\'t, and I don\'t understand why.

Answer 1

Php can be confusing in this regard you should read this.

What's also confusing is that you can call non static functions with the :: symbol. This is very strange when you come from Java. And it certainly surprised me when I first saw it.

For example:

class Car
{
    public $name = "Herbie 
";

    public function drive()
    {
        echo "driving 
";
    }

    public static function gas()
    {
        echo "pedal to the metal
";
    }
} 

Car::drive(); //will work
Car::gas(); //will work

$car = new Car();
$car->drive(); // will work
$car->gas(); //will work

echo $car->name; // will work
echo Car::$name; // wont work error

As you can see static is very loose in php. And you can call any function with both the -> and the :: symbols. But there is a difference when you call with :: there is no $this reference to an instance. See example #1 in the manual.