First of all: dependency injection is GREAT!

Several of Symfony2’s core services depend on tags to recognize which user-defined services should be loaded, notified of events, etc. For example, Twig uses the tag twig.extension to load extra extensions. It would also be great to use tags in case your service implements some kind of “chain”, in which several alternative strategies are tried until one of them is successful. In this post I use the example of a so-called “TransportChain”. This chain consists of a set of classes which implement the Swift_Transport interface. Using the chain, the mailer may try several ways of transport, until one succeeds. This post focuses on the “dependency injection” part of the story. The implementation of the real TransportChain is left to the reader (as an exercise ;)).

Last week I was one of the several hundreds of PHP developers who traveled “all te way” to Amsterdam for the Dutch PHP Conference 2010. Though I had the impression that many PHP developers are using the symfony framework for their web applications, the speakers at this conference were friendlier towards the “father of the framework”, Fabien Potencier, than towards the framework itself. Fabien is a much admired developer himself, who is very conscious about software architecture, latest trends in PHP development and also is aware of the importance of fully covering the framework’s code with unit tests. In this article I will try to apply to the symfony framework, several comments on PHP programming and frameworks that I heard during this conference.