Different ways to access methods

Question

I have seen that there are two different ways to access methods within a class. Are there any differences in behaviour, or are they purely alternative syntaxes for the same action?

$a = new A();
$a->foo();

A::foo();

Answer 1

You can't just use one or the other. :: is for static methods and variables, whereas -> is for instance methods and variables. This is "inspired" from C++ syntax.

class A {
    public function __construct() {}
    public function foo() {}
}
$a = new A();
$a->foo();
// Or use the shorter "new A()->foo()";
//   It won't return typeof(A), it will return what foo() returns.
// The object will still be created, but the GC should delete the object

or

class A {
    public static function foo() {}
}
A::foo();

According to DCoder, :: can be used for calling parent methods, but I don't know this for sure.

class B {
    public function __construct() {}
    public function foo() {}
}
class A extends B {
    public function __construct() {
        // Code
        parent::__construct()
    }
    public function foo() {
        // Code
        parent::foo()
    }
}