I learned to program with BASIC back when I was twelve. I would write elaborate programs and run them. Invariably, they would surprise me by failing to do what I expect. I would struggle for a time, but I’d eventually give up and just accept that whatever “bugs” I had created were there to stay.
It would take me a decade to learn how to produce reliable and useful software. To this day, I still get angry with people who take it for granted that software should do what they expect without fail.
In any case, I eventually graduated to something better: Turbo Pascal. Turbo Pascal was a great programming language coupled with a fantastic programming environment that is comparable, in many ways, to modern integrated development environments (IDEs). Yet it is three decades old. It had something impressive: you could use a “debugger”. What this means is that you could run through the program, line by line, watching what happened to variables. You could set breakpoints where the program would halt and give you control.
At the time, I thought that programming with a debugger was the future.
I am not alone. In five minutes, I was able to find several famous programmers who took positions against debuggers or who reported barely using them.
- Linus Torvalds, the creator of Linux, does not use a debugger.
- Robert C. Martin, one of the inventors of agile programming, thinks that debuggers are a wasteful timesink.
- John Graham-Cumming hates debuggers.
- Brian W. Kernighan and Rob Pike wrote that stepping through a program less productive than thinking harder and adding output statements and self-checking code at critical places. Kernighan once wrote that the most effective debugging tool is still careful thought, coupled with judiciously placed print statements.
- The author of Python, Guido van Rossum has been quoted as saying that uses print statements for 90% of his debugging.
I should make it clear that I do not think that there is one objective truth regarding tools. It is true that our tools shape us, but there is a complex set of interactions between how you work, what you do, who you work with, what other tools you are using and so forth. Whatever works for you might be best.
However, the fact that Linus Torvalds, who is in charge of a critical piece of our infrastructure made of 15 million lines of code (the Linux kernel), does not use a debugger tells us something about debuggers
Anyhow, so why did I stop using debuggers?
Debuggers were conceived in an era where we worked on moderately small projects, with simple processors (no thread, no out-of-order execution), simple compilers, relatively small problems and no formal testing.
For what I do, I feel that debuggers do not scale. There is only so much time in life. You either write code, or you do something else, like running line-by-line through your code. Doing “something else” means (1) rethinking your code so that it is easier to maintain or less buggy (2) adding smarter tests so that, in the future, bugs are readily identified effortlessly. Investing your time in this manner makes your code better in a lasting manner… whereas debugging your code line-by-line fixes one tiny problem without improving your process or your future diagnostics. The larger and more complex the project gets, the less useful the debugger gets. Will your debugger scale to hundreds of processors and terabytes of data, with trillions of closely related instructions? I’d rather not take the risk.
My ultimate goal when work on a difficult project is that when problems arise, as they always do, it should require almost no effort to pinpoint and fix the problem. Relying on a debugger as your first line of defense can be a bad investment, you should always try to improve the code first.
If you dive into the bug, you tend to fix the local issue in the code, but if you think about the bug first, how the bug came to be, you often find and correct a higher-level problem in the code that will improve the design and prevent further bugs.
I don’t want to be misunderstood, however. We need to use tools, better tools… so that we can program ever more sophisticated software. However, running through the code line-by-line checking the values of your variables is no way to scale up in complexity and it encourages the wrong kind of designs.