Become A Better Programmer - How To Read Source Code

Sat 19 July 2014

Filed under Blog

Tags practice reading command-line-parser

Reading soure code has many benefits. You will discover new constructs and libraries, develop empathy for others maintaining your code, and most importantly learn how to structure your code so that it doesn't fall over from internal complexity.

There is one drawback though, reading source code is darned hard. When I look at a new code base, this sickening feeling washes over me. My mind just doesn't want to dive into this perceived mess.

This is (hopefully) a normal response. When our brains sees too much novelty, it just tends to shy away. There is nothing for our amazing biological pattern matching machine to latch onto. The abstractions are all new. It's never seen the class names before. Where does execution even start?

The general tips I can offer are the following: 1. Find and establish an initial base for your mind to latch onto. Usually the main entry point. 2. Start from your base and explore the major features. 3. Take notes on what you've seen.

Start At The Beginning.

The trick is to give your mind a starting point. Here is what I do. I just run the program with the -h option and invoke the help. Then I copy one of the help strings and do a search over the code base to see where this help text is located. Usually the help invocation is pretty close to where the main entry point to the program is.

Identify The Shape Of The Program

Once I've found the main entry point, I run a few toy examples included in the documentation. Then I try to trace the main blocks of code to just get a rough sketch of how the piece fit together.

Is there a manager that invokes a ton of helper functions and classes? Are there a bunch of classes that act as peers and hand control off between each other? Is there a main queue of tasks that gets consumed over time?

Getting the big picture helps you slot in the little pieces. You tend to get overwhelmed by the details if you try to forge ahead without understanding the main flow.

Take Notes

I tend to take notes right in the source code. When writing I use a special comment character (e.g #=> instead of the typical #) so that I can distinguish between my own notes and the original author's comments.

Make a note on all the clever tricks, confusing flows, beautiful usgae of programming constructs, and anything else you want to remember. If you're stuck, you can also make a note about coming back to that particular section.

By writing down your thoughts, you're really making that piece of source code your own. Over time, the constructs you pick up will start leaking into your own works.

Becoming Your Own Person

Learning to program is a continuous process of reading code and writing code. By exposing yourself to a variety of styles, you'll eventually develop a unique perspective and voice.

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