S.O.L.I.D. presentation conducted!

Last Friday I conducted S.O.L.I.D. principles presentation in my company, EPAM Systems.


While I was working at Tau Craft, I tried to do it step-by-step, explaining one principle at a time.

But I stopped on the second stage -- Open-Closed Principle as I felt that I need to rethink my approach, them postponed it until this time.

Now I took a completely different approach supplying each principle with a huge amount of examples in Visual Studio 2012.

Combining live coding with theoretical part the whole things seemed more logical and memorable, so my auditory was quite satisfied (that was demonstrated by high course rates).

Let's see one good metaphor for Open-Closed Principle:

OCP

I found it during preparation and now believe that it's the best example I have ever seen! :)

There were some problems with Liskov Substitution Principle, but it went just fine thought it still needs to be improved (will do it).

The most debatable case was Dependency Inversion Principle:

DIP

We spent plenty of time discussing of how much granularity should be used.

And yes! Remember one thing: Dependency Inversion is not equal to Dependency Injection! They are often mixed out, but they should not! :)
Let's have a look at an example.

Before DIP applied:

 On this picture the layering is ok (consider namespace as an assembly/module).

UI depends on Business, Business depends on Data Access.

The DIP violated because two things:

1. UI depends on low-level detail (uses PointOfSaleTerminal class.
2. No abstractions at all.

After fixing we acquired the following picture:

 In this case dependencies were TRULY INVERTED!

All modules now depends on interface class.

I must mention that the key idea is that Dependency Injection is just a tool to implement Dependency Inversion.

You can find a good article about it in Dependency Injection is NOT The Same As The Dependency Inversion Principle by Derick Bailey