PHP difference in accessing class methods

What's the difference betw开发者_开发百科een $foo->bar() and $foo::bar()?

$foo::bar() is a call of the static method bar(), that means the object $foo was not instanciated by the __construct() method.

When calling $foo->bar(), the object $foo has to be instanciated before! Example:

$foo = new Foo; // internally the method __constuct() is called in the Foo class!
echo $foo->bar(); 

Often you don't call a static method on a existing object like in you example ($foo), you can call it directly on the class Foo:

 Foo::bar();

With the first one

$foo->bar();

you call (object) methods, whereas with

Foo::bar();

you call class (static) methods.

Its possible to call class methods on objects. That is, what your second example does. So this

$foo = new Foo;
$foo::bar();

is identical to

Foo::bar();

or even

$classname = get_class($foo);
$classname::bar();

Update: Missed something $foo can also just be a string with a classname.

$foo = 'Baz';
$foo::bar(); // Baz::bar();