How to make a const-correct codebase in 4300 easy steps

One of the codebases that I work on is theoretically C++, but if you peer under the hood, it looks more like 1990-vintage C. It’s 500 KLOC of almost purely procedural code, with lots of structs and few true objects. More dusty and brittle than I’d like.

Image credit: Tim Gillin (Flickr)

I am not a C++ bigot; I first began to do serious, professional coding in C, not long after this codebase got its start. I understand the C-isms pretty well. And although I think Linus got carried away in his rant about the ugliness of C++, I can appreciate the ways that lean C sometimes makes its descendant look ugly and inefficient. (Though C++11 and 14 are making this less true…)

This means that I don’t consider the C-like style of this particular codebase a fatal flaw, in and of itself.

However, since my early coding adventures I’ve been converted to the advantages of OOP for complex projects and large teams, and I’ve also accumulated a lot of battlescars around multithreading. Our codebase needs OOP to solve some encapsulation antipatterns, and it needs RAII and C++11-style mutexing in the worst way. Its old, single-threaded mindset makes far too many things far too slow and error-prone.

A few months ago, we decided to make an investment to solve these problems.

To do it right, I had the team add a story to our scrum backlog about making the codebase const-correct. And therein lies a tale worth recounting…

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On bread recipes, maps, and intentions

[I’ve been quiet for the past three weeks–not because I have less that I want to talk about, but because I have more. Major wheels turning in my head. I’m having a hard time getting from the “intuited ideas” mode to the “crisp enough to put it in writing” mode, though. Consider this a down payment on some future discussions…]

One of my mother’s talents is bread-making. She’s been kneading and baking and pulling beautiful loaves out of the oven for as long as I can remember. Bread is one of the ways she says “I love you” to family and friends.

A few years back, she created a cookbook full of family recipes, and gave one to each adult child for Christmas. I was struck by how she began the bread section. Instead of launching right into the recipes, she included a couple of pages of “bread theory”, if you will. The section about water is typical:

“Water — Just about any edible liquid could be used as the base for bread. Some that come to mind are vegetable cooking water, potato water, milk, and so on. There is no problem with substituting any of these for liquid called for in a recipe, but you should keep in mind that if the liquid is salty, the salt should be adjusted; if the liquid is sweet, the sugar should be adjusted… Fresh milk can be a problem because of enzymes that would prevent yeast action. For this reason, most old recipes that call for milk specify that the milk be scalded first. This isn’t necessary if you are using water and powdered milk, but remember that the mechanics of the recipe probably depend on at least warm milk (so use warm or even hot water).”

If you’re wondering why I am writing about bread recipes in this blog that focuses on software craftsmanship, consider how much that paragraph resembles a really high-value comment in source code.

It has to do with principles and intentions.

Software is all about recipes, right?

Recipes are a lot like software algorithms (especially in imperative programming styles): First, do this; next, do that; wait 25 minutes; return new Loaf()… We even talk about “recipes” and “cookbooks” when we make catalogs of software techniques.

How is this metaphor instructive… or worrisome?

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Why Exceptions Aren’t Enough

(This post is a logical sequel to my earlier musings about having a coherent strategy to handle problems.)

Back in the dark ages, programmers wrote functions that returned numeric errors:

if (prepare() == SUCCESS) {

This methodology has the virtue of being simple and fast. We could switch based on the error code. A “feature” of our apps was that our users could google an error code to see if they had company:

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However, as we wrote code, we sometimes forgot to check errors, or tell users about them:


Admit it; you’ve written code like this. So have I. The mechanism lets a caller be irresponsible and ignore the signal the called function sends. Not good. Even if you are being responsible, the set of possible return values is nearly unbounded, and you get subtle downstream bugs if a called function adds a new return value when a caller is switching return values.

Another problem with this approach to errors Continue reading