When to use self over $this?

Question

In PHP 5, what is the difference between using self and $this?

When is each appropriate?

Answer 1

Additionally since $this:: has not been discussed yet.

For informational purposes only, as of PHP 5.3 when dealing with instantiated objects to get the current scope value, as opposed to using static::, one can alternatively use $this:: like so.

http://ideone.com/7etRHy

class Foo
{
    const NAME = 'Foo';

    //Always Foo::NAME (Foo) due to self
    protected static $staticName = self::NAME;

    public function __construct()
    {
        echo $this::NAME;
    }

    public function getStaticName()
    {
       echo $this::$staticName;
    }
}

class Bar extends Foo
{
    const NAME = 'FooBar';

    /**
     * override getStaticName to output Bar::NAME
     */
    public function getStaticName()
    {
        $this::$staticName = $this::NAME;
        parent::getStaticName();
    }
}

$foo = new Foo; //outputs Foo
$bar = new Bar; //outputs FooBar
$foo->getStaticName(); //outputs Foo
$bar->getStaticName(); //outputs FooBar
$foo->getStaticName(); //outputs FooBar

Using the code above is not common or recommended practice, but is simply to illustrate its usage, and is to act as more of a "Did you know?" in reference to the original poster's question.

It also represents the usage of $object::CONSTANT for example echo $foo::NAME; as opposed to $this::NAME;