A new buzzword in the PHP circles is Fluent Interfaces, which is not really new, but a way to chain methods of an object together. Here’s an example from Mike Naberezny which shows the regular way and the Fluent way:

< ?php private function makeNormal(Customer $customer) {
$o1 = new Order();
$customer->addOrder($o1);
$line1 = new OrderLine(6, Product::find(‘TAL’));
$o1->addLine($line1);
$line2 = new OrderLine(5, Product::find(‘HPK’));
$o1->addLine($line2);
$line3 = new OrderLine(3, Product::find(‘LGV’));
$o1->addLine($line3);
$line2->setSkippable(true);
$o1->setRush(true);
}
?>

The fluent way: < ?php private function makeFluent(Customer $customer) {
$customer->newOrder()
->with(6, ‘TAL’)
->with(5, ‘HPK’)->skippable()
->with(3, ‘LGV’)
->priorityRush();
}
?>

For those who do not recognize this particular buzzword fluent interfaces is a way of chaining methods of an object together. By having a method return a reference to the object itself, return $this; you chain methods together like this $this->methodOne()->methodTwo()->methodThree();. This can make your code easier to read, and that is the point of using fluent interfaces, making your code easier to read.

via: Zend Developer Zone

Andi Gutmans tells us where to use this pattern:

Of course there are no definitive answers but I suggest to consider the following points:
a) Use your intuition. If you don’t feel this will address the 95% of common use-case for using your interface, then it’s probably not the right solution for what you’re trying to accomplish.
b) As Paul noted, if in the common use-case you don’t have all the necessary data available to complete the task in one go, you should think twice about doing it.
c) Probably the most important point: It really has to read well in your language (e.g. English), preferably as a complete sentence. If you can’t read the code out aloud then it’s probably not what you want.

Link: Andi Gutmans’ Weblog | Fluent Interfaces

Mark Naberezny has an helloworld example at his blog which shows you how to build a fluent interface:

In PHP 5 terms, a fluent interface to an object is one where the setter methods return an object handle. It is perhaps simplest to always return $this, however any object handle can be returned. Here’s a simple PHP class that demonstrates how a fluent interface is built:

< ?php
class Fluent {
public function hello() {
echo ‘hello ‘;
return $this;
}
public function world() {
echo ‘world’;
return $this;
}
}
$fluent = new Fluent();
$fluent->hello()
->world();
?>

Link: Fluent Interfaces in PHP