Monthly Archives: December 2012

Dec 04 2012
2 Comments
Coding, Design Patterns

The Visitor Pattern in PHP

Implementing the Visitor Pattern requires the ability to dynamically determine the type of the Visitor and the type of the “Element” (aka: object receiving the visitor).

In PHP (>= 5.0.0), this can easily be achieved with the get_class() function as we will see shortly.

Let’s start by looking at how the Visitor Pattern will look within user code;

$updateVisitor = new UpdateVisitor();
$deleteVisitor = new DeleteVisitor();
$element = new Foo();

$element->visit($updateVisitor);
$element->visit($deleteVisitor);

Looking at the UpdateVisitor class, we want the visitFoo() function to be called;

interface Visitor { }
class UpdateVisitor implements Visitor {
    public function visitFoo(Foo $theElement) {
        // ...
    }
}

You may already be (correctly) thinking “Why not just call $updateVisitor->visitFoo($element) directly?”.
Continue reading →

Tagged , , ,