Saturday, November 24, 2007

3 Pass Coding

Back in the day at Microsoft we used to look for and train developers who were 1 pass coders. In today's world everyone is a 3 pass coder and they are starting to drag me down with them.

Let me explain the difference between a 1 pass and a 3 pass coder.

When you are writing code there are several layers (or aspects) of design and implementation activity that have to be balanced. Firstly, you have the very simple, but often disputed, question of whether the code will meet a functional objective. This is often referred to Working. If the code won't perform the purpose the code is intended for it Doesn't Work and the rest of its qualities aren't relevant. Assuming that it can be made to fulfill its intended purpose (i.e. it Works), then the other two aspects suddenly become important.

The next most tangible aspect of coding is the speed at which the code will execute or process units of work, transactions, operations, etc. Regardless of the velocity or metrics implied, the measure of this aspect of coding is generally called Performance. Making something Work is the first step which is immediately followed by does it Work Fast.

Lastly you have a host of intangibles of varying degrees of importance. There can be many tangible expressions of these intangible attributes used by different people at different times. The number of comments, the readability of the control flow, the robustness of the error and state management, and the lack of logic or bounding bugs; are all examples and all of which are related. We put these closely-coupled items in a big bucket called Quality. This may also referred to as Maintainability, Elegance, etc. If you can make it Work, and make it Work Fast, can you make it Work Correctly?

Now when someone starts out coding, they generally are capable of keeping only one layer in their mind at a time. They start by making the code Work. They just want to see it do what they think it should do. Of course, once it does that, then they immediately concern themselves with making it Work Fast. It is about this time that consumers of their code start exercising the possibilities and uncovering flaws and boundaries of the code. So a review of code usually focused on specific bugs or concerns is undertaken until eventually it is determined the code must Work Correctly. This lifecycle usually involves 3 distinct reviews or Passes on the code. It is written, then reviewed for performance or capacity, then again for bugs and boundaries.

On the other hand, a 1 Pass coder will have such a clear picture in mind of the code, the control of flow, the logic loops, the impediments and enhancements to speed, the boundary conditions and bug potentials, that the exercise is compressed into a single Pass of coding. All the work is done upfront in the design and in the construction of each line so that intangibles are caught during the initial pass.

At least that's how we used to do it. It's how I used to do it.

Now engineers are so woefully under-skilled. They aren't forced to learn logic or bit math. They didn't take any classes on algorithm design or perform exercises on bug potentials. They just want to see it Work and then have testers tell them what else needs fixing. If you want it to Work Fast they just buy bigger boxes or more of them. The days of discipline are gone.

When I have to oversee their work or explain an implementation I find myself being forced to speak in terms of what it takes to make it Work because the other layers trip them up. If I show them tight, elegant code with robust error and state management and efficient control of flow, they can't read or follow it. When I assign bugs they want to debug and watch the code execute because they can't find the bugs by reading the code. I have to worry about losing my own skills just working alongside them.

Yesterday for a personal coding project I came across a bug running the program and my first thought was to set a breakpoint and see what happened. I wanted to slap myself out of the chair! I'm better than that. I can READ and understand code. Which doesn't mean I don't take advantage of the debugger, but it shouldn't be my first thought. I'm a 1 Pass coder and I intend to stay that way.

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