Difference between :: and -> in PHP

Question

I always see people in serious projects use :: everywhere, and -> only occasionally in local environment.

I only use -> myself and never end up in situations when I need a static value outside of a class. Am I a bad person?

As I understand, the only situation when -> won't work is when I try following:

class StaticDemo {  
    private static $static  
}

$staticDemo = new StaticDemo( );

$staticDemo->static; // wrong  
$staticDemo::static; // right

But am I missing out on some programming correctness when I don't call simple public methods by :: ?

Or is it just so that I can call a method without creating an instance?

Answer 1

The double colon is used when you don't instantiate a class

class StaticDemo {...};
StaticDemo::static

if you do instantiate, use -->

class StaticDemo {...};
$s = new StaticDemo();
$s->static;

This is explained further at http://php.net/manual/en/language.oop5.patterns.php