In a new post to his blog, Sebastian Bergmann mentions a new effort he's undertaken - the porting of the Hamcrest library of matcher objects to PHP.

I have begun to port Hamcrest, which provides a library of matcher objects (also known as constraints or predicates) allowing "match" rules to be defined declaratively, to be used in other frameworks. Typical scenarios include testing frameworks, mocking libraries and UI validation rules, to PHP.

The hamcrest-php project compliments other current hamcrest-related projects and his ultimate goal is to make it available to the PHPUnit testing community (as well as with the PHPMock effort).

While attending a code camp for Xenerix, Ivo Jansch decided to challenge himself to create a way to implement Object Constraint Language functionality in PHP objects.

To give a practical example: if you have a class 'Creditcard', you could define the constraints 'self.limit > 0' when withdrawing an amount. While the goal of the code camp was to do some nifty things with OCL and Ruby, I wanted to see if I could create a method to easily implement OCL constraints in arbitrary PHP objects.

He structures his example similar to the one provided, making CreditCard and Person classes with constraints on the person's name, withdrawing past the expire date of the card and the keeping the limit of the card above zero. He created a OCL wrapper class to handle most of the hard work, but he provides the code examples you'll need to see it in action, complete with constraints.