Whats the difference between -> and :: in OOP

Question

Trying to find some information on this but am unable to get any results probably due to the chars used.

What is the difference between the following as from what I gather they do the same thing.

$classname->function()
Classname::function()

Does the second example automatically instantiate the object?

This has been covered a million times. Where is your PHP book? — Lightness Races in Orbit, Feb 07 '12 at 11:36
possible duplicate of [Reference - What does this symbol mean in PHP?](http://stackoverflow.com/questions/3737139/reference-what-does-this-symbol-mean-in-php) — hakre, Jul 12 '12 at 16:44

score 3 · Accepted Answer · edited May 23 '17 at 12:27

3

The former (->) is used to invoke non-static members (methods or functions / properties or variables), while the later (::) is used to invoke static members.

Non-static:

class foo{
  function bar(){ echo 'test';  }
}

$foo = new foo();
$foo->bar();

Static:

class foo{
  static function bar(){ echo 'test';  }
}

foo::bar(); // no class initialization needed

See this question for more info:

PHP: Static and non Static functions and Objects

To better understand the concept, you should check out what static methods are and how they are different from non-static.

edited May 23 '17 at 12:27

Community

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answered Feb 07 '12 at 11:36

Sarfraz

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That's really cleared things up for me, I didn't know they had different names to be honest. Many thanks though. – Shane Jones Feb 07 '12 at 12:25

score 1 · Answer 2 · answered Feb 07 '12 at 11:33

1

No, the second one is calling a static method. Check here.

answered Feb 07 '12 at 11:33

xdazz

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score 1 · Answer 3 · answered Feb 09 '12 at 03:34

The second example doesn't automatically instantiate the object. So in the second way of calling, if you had used $this in the function, you will get a error like : PHP Fatal error: Using $this when not in object context.
In general, -> is used to call a non-static method, :: is used to call a static method.
But it's not so strict in php. For example:

error_reporting(E_ALL);
class A {
    public static function staticFunc() {
        echo "static";
    }

    public function instanceFunc() {
        echo "instance";    
    }
}

A::instanceFunc(); // echo "instance"
$a = new A();
$a->staticFunc();  // echo "static"

The two method called above run successfully.
Because php always implementing new features in a progressive way, to ensure compatibility, which may resulted in some detail doesn't cared much about. But if you set the error_reporting level to E_STRICT , you will find a E_STRICT error like this:
Strict Standards: Non-static method A::instanceFunc() should not be called statically

The only difference in these two ways is that: when you calling a method with :: , you can't use variable $this .

But it's still recommended you to use these two ways strict as in other Object Oriented language.
You can get more information in http://www.php-internal.com/book/?p=chapt05/05-02-class-member-variables-and-methods

Whats the difference between -> and :: in OOP

3 Answers3