On the Qafoo blog today Tobias Schlitt talks about dynamic dispatch, what he calls a "fundamental concept of OOP" to help provide clean, clear interfaces in the code.
I want to use this blog post to illustrate the concept of dynamic dispatch which I use a lot recently to motivate creating clean OO structures in my trainings. In my experience, this helps people to understand why we want to write code in this way. After that I will show why traits are bad in this direction.
He explains the concept of "dynamic dispatch" by starting from the beginning...with procedural PHP code. He looks at the usual flow of this kind of application that call shared functions in a "top down" fashion. He looks at what would happen if new logging needs were introduced (use a new method? patch the current one?) and the dependencies that can be introduced because of it. With this in mind, he continues and talks about how the "dynamic dispatch" happens during the code execution, splitting the log request based on the information it's given instead of different implementations for each. He points out that using a trait doesn't allow for this abstraction and instead embeds the code into the class itself, re-introducing the original problem.