A Software Design Pattern which brings the principles of Inheritance, Encapsulation and Polymorphism one level up from the Class level to the Subsystem level, and offers a way of realizing relationships between classes so as to achieve dependency inversion by means of propagation instead of injection.

Part 1: Dependency Inversion

The software that we write often invokes other software to get parts of the job done. These are known as Services or Dependencies. If Class A is making use of some Class B, then Class A depends on Class B, so Class B is a dependency of Class A.

The principle of Dependency Inversion says that a class should not contain any direct calls to specific instances of any of its dependencies. Instead, it should receive these instances as parameters during initialization.

That’s all very nice, but passing dependencies around can become quite a complicated business, and in large systems it can become a nightmare.

Let me start with a couple of pedantic definitions; stay with me, the beef follows right afterwards.

Conventional wisdom says that validation is different from error checking.

• Validation is performed at the boundaries of a system, to check the validity of incoming data, which is at all times presumed to be potentially invalid. When invalid data is detected, validation is supposed to reject it. Validation is supposed to be always on, you cannot switch it off on release builds and only have it enabled on debug builds.
• Error checking, on the other hand, is performed inside a system, checking against conditions that should never occur, to keep making sure that everything is working as intended. In the event that an error is encountered, the intent is to signal a catastrophic failure. Essentially, the term Error Checking is shorthand for Internal Error Checking. It can be implemented using assertions, thus being active on the debug build only, and having a net cost of zero on the release build.

So far so good, right?

As the screenshot proves.

What to reply to a non-programmer who thinks that testing is unnecessary or secondary

At some point during his or her career, a programmer might come across the following argument, presented by some colleague, partner, or decision maker:

Since we can always test our software by hand, we do not need to implement Automated Software Testing.

Apparently, I reached that point in my career, so now I need to debate this argument. I decided to be a good internet citizen and publish my thoughts. So, in this post I am going to be deconstructing that argument, and demolishing it from every angle that it can be examined. I will be doing so using language that is easy to process by people from outside of our discipline.

In this post I am documenting sightings of these red heart stickers.

If anyone knows what these are, who sticks them, what for, please do let me know.

If you try visiting The Pirate Bay from Holland nowadays, you are very likely to be disappointed. Your internet provider will most probably block your access with a page like this: https://blocked.t-mobilethuis.nl/

This is, of course, completely unacceptable.

But while we are sitting around wondering when the revolution will start so that we can round up all those responsible for this situation and send them to the forced labor camps, it would be nice if we had some means of bypassing the block.

Here is how: