Start at the End

Any software development effort involves the conveying of information, but it’s easy for the important information to be hidden by related (but less important) stuff. Starting at the end is a good way to focus on the information that matters most.

Drawing Maps

In the days before Google Maps, we used to ask other people for directions to places we wanted to go, and often someone would volunteer to draw a map on paper. After taking part in many of these information exchanges, I observed that most people (including myself), when drawing a map, start at the beginning. That is, they start the drawing at the traveler’s point of origin and proceed from there to the destination.

The result was almost always adequate for the intended purpose of getting the traveler from point A to point B, but I noticed that the destination often ended up being crammed into a corner of the page, almost as if it were an afterthought rather than the most important piece of information on the map.

Now it certainly makes sense to draw a map in this fashion. I imagine that the main reason for doing it this way is that when drawing a map we imagine ourselves actually taking the trip we’re describing. We start at the beginning of our imaginary trip and eventually find our way to the destination.  And unless we begin with an inordinately large piece of paper, or are particularly good at allocating space ahead of time, we end up with a map that contains extra information we really don’t need, while details of the destination are omitted because we run out of room.

So I started drawing maps from the end. The first place I put on a map is the destination. From there I work backwards, drawing the streets leading to the destination. Then, if I have room, I draw the highways leading back to the city of origin. The result is a map that emphasizes the important details.

Communicating Technical Information

I’ve noticed a similarity between the way people draw maps and the way they convey technical information. That is, they often tend to start at the beginning and proceed in chronological order to the end.

Just as in map drawing, this approach makes a certain amount of sense. It’s natural for people to convey information in the order in which they discovered or developed it. The communication of the information is kind of a chronological account of the original experience of creation.

The problem is, it’s the end (the destination) that I’m most interested in. I tend to think of the result as the important part, with everything leading up to it being more like “supporting information” which I may or may not want (or even need) to know.

In other words, I tend to get lost in the details of the journey, when what I’m really interested in is where I’m going to end up.

Writing Software

I used to write code from top to bottom. That is, when I wrote a method I would start at the top of the method, and write lines of code in the order in which they would be executed. It made sense, in a way, because I was taught to read and write English from top to bottom. It seemed the natural way to go about it. Unfortunately this approach tended to introduce unnecessary code into the method that had to be stripped out later.

Now when I write software, I like to start at the end. When I write a unit test, for example, I start by writing the assert statement, even if it asserts against objects that don’t yet exist. I start with the assertion, then I see what the assertion requires and I write a line of code above it to satisfy those requirements. If satisfying those requirements introduces new requirements, I write a line of code above that, and so on.

The result is a unit test that carries no extra baggage, no superfluous information, with an emphasis on the most important part, the assertion.

The assertion in a unit test is analogous to the destination on a map. Both are the most important pieces of information. Both make excellent starting points.