Why return $this in setter methods?

Question

Examining Zend Framework, I found that all setter methods (of those I’ve examined) return the instance of the class it lives in. It doesn\'t only set a value but also return

Answer 1

It's so that method calls on an object can be "chained", like this.

$obj -> setFoo ('foo') -> setBar ('bar') -> setBaz ('baz') -> setFarble ('farble');

Answer 2

The return $this allows the chaining of methods like:

$foo->bar('something')->baz()->myproperty