This is my first entry into #iDevBlogADay. It all started very innocently with a suggestion from Miguel, but the ball got rolling pretty quickly. The idea is to have one independent iPhone game developer write a blog entry each day of the week. At first we thought we would be hard-pressed to get 7 developers, but it’s starting to seem we might have multiples per day!

Check out the new sidebar with all the #iDevBlogADay blogs. We’re also putting together a common RSS feed if you want to subscribe to that instead.

Writing is addictive, so don’t be surprised if this once-a-week minimum turns into multiple-times-a-week.

Every developer who’s been working on a team for a while is able to tell the author of a piece of code just by looking at it. Sometimes it’s even fun to do a forensic investigation and figure out not just the original author, but who else modified the source code afterwards.

What I find interesting is that I can do the same thing with my own code… as it changes over time. Every new language I learn, every book I read, every bit of code I see, every open-source project I browse, every pair-programming session, every conversation with a fellow developer leaves a mark behind. It slightly changes how I think of things, and realigns my values and priorities as a programmer. And those new values translate into different ways to write code, different architectures, and different coding styles.

It never happens overnight. I can’t recall a single case where I changed my values in a short period of time, causing dramatic changes to my coding style. Instead, it’s the accumulation of lots of little changes here and there that slowly shifts things around. It’s like the movement of the Earth’s magnetic pole: very slow, but changes radically over time (although maybe just a tad bit faster).

Why Talk About Coding Styles

Coding style in itself is purely a personal thing, and therefore, very uninteresting to talk about. However, in its current form, my coding style goes against the grain of most general modern “good practices”. A few weeks ago I released some sample source code and it caused a bit of a stir because it was so unconventional. That’s when I realized it might be worth talking about it after all (along with George bugging me about it), and especially the reasons why it is the way it is.

Before I even start, I want to stress that I’m not advocating this approach for everybody, and I’m certainly not saying it’s the perfect way to go. I know that in a couple of years from now, I’ll look back at the code I’m writing today and it will feel quaint and obsolete, just like the code I wrote during Power of Two Games looks today. All I’m saying is that this is the style that fits me best today.

Motivation

This is my current situation which shapes my thinking and coding style:

All my code is written in C and C++ (except for a bit of ObjC and assembly).

It’s all for real-time games on iPhone, PCs, or modern consoles, so performance and resource management are very important.

I always try to write important code through Test-Driven Development.

I’m the only programmer (and only designer).

Build times in my codebase are very fast.

And above all, I love simplicity. I try to achieve simplicity by considering every bit of code and thinking whether it’s absolutely necessary. I get rid of anything that’s not essential, or that’s not benefitting the project by at least two or three times as much as it’s complicating it.

How I Write Today

So, what does my code look like these days? Something like this (this is taken from a prototype I wrote with Miguel of Mystery Coconut fame):

namespace DiverMode { enum Enum { Normal, Shocked, Inmune, }; } struct DiverState { DiverState() : mode(DiverMode::Normal) , pos(0,0) , dir(0) , o2(1) , boostTime(0) , timeLeftInShock(0) , timeLeftImmune(0) {} DiverMode::Enum mode; Vec2 pos; float dir; float o2; float boostTime; float timeLeftInShock; float timeLeftImmune; }; namespace DiverUtils { void Update(float dt, const Vec2& tiltInput, GameState& state); void Shock(DiverState& diver); void StartSprint(DiverState& diver); void StopSprint(DiverState& diver); }

The first thing that stands out is that I’m using a struct and putting related functions in a namespace. It may seem that’s just a convoluted way of writing a class with member functions, but there’s more to it than that.

By keeping the data in a struct instead of a class, I’m gaining several advantages:

I’m showing all the data there is and how big it is. Nothing is hidden.

I’m making it clear that it’s free of pointers and temporary variables.

I’m allowing this data to be placed anywhere in memory.

The fact that the functions are part of a namespace is not really defensible; it’s pure personal preference. It would have been no different than if I had prefixed them with DriverUtils_ or anything else, I just think it looks clearner. I do prefer the functions to be separate and not member functions though. It makes it easier to organize functions that work on multiple bits of data at once. Otherwise you’re stuck deciding whether to make them members of one structure or another. It also makes it easier to break up data structures into separate structures later on and minimize the amount of changes to the code.

Probably one of the biggest influences on me starting down this path was the famous article by Scott Meyers How Non Member Functions Improve Encapsulation. I remember being shocked the first time I read it (after having read religiously Effective C++ and More Effective C++). That reasoning combined with all the other changes over the years, eventually led to my current approach.

Since everything is in a structure and everything is public, there’s very little built-in defenses against misuse and screw-ups. That’s fine because that’s not a priority for me. Right now I’m the only programmer, and if I work with someone else, I expect them to have a similar level of experience than me. Some codebases written with a defensive programming approach have an amazing amount of code (and therefore complexity) dedicated to babysitting programmers. No thanks. I do make extensive use of asserts and unit tests to allow me to quickly make large refactorings though.

Another thing to note that might not be immediately obvious from the example above is that all functions are very simple and shallow. They take a set of input parameters, and maybe an output parameter or just a return value. They simply transform the input data into the output data, without making extensive calls to other functions in turn. That’s one of the basic approaches of data-oriented design.

Because everything is laid out in memory in a very simple and clear way, it means that serialization is a piece of cake. I can fwrite and fread data and have instant, free serialization (you only need to do some extra work if you change formats and try to support older ones). Not only that, but it’s great for saving the game state in memory and restoring it later (which I’m using heavily in my current project). All it takes is this line of code:

oldGameState = currentGameState

This style is a dream come true for Test-Driven Development (TDD). No more worrying about mocks, and test injections, or anything like that. Give the function some input data, and see what the output is. Done! That simple.

One final aspect of this code that might be surprising to some is how concrete it is. This is not some generic game entity that hold some generic components, with connections defined in XML and bound together through templates. It’s a dumb, POD Diver structure. Diver as in the guy going swimming underwater. This prototype had fish as well, and there was a Fish structure, and a large array of sequential, homogeneous Fish data. The main loop wasn’t generic at all either: It was a sequence of UpdateDivers(), UpdateFish(), etc. Rendering was done in the same, explicit way, making it extra simple to minimize render calls and state changes. When you work with a system like this, you never, ever want to go back to a generic one where you have very little idea about the order in which things get updated or rendered.

Beyond The Sample

To be fair, this sample code is very, very simple. The update function for a reasonable game element is probably larger than a few lines of code and will need to do a significant amount of work (check path nodes, cast rays, respond to collisions, etc). In that case, if it makes sense, the data contained in the structure can be split up. Or maybe the first update function generates some different output data that gets fed into later functions. For example, we can update all the different game entities, and as an output, get a list of ray cast operations they want to perform, do them all in a later step, and then feed the results back to the entities either later this frame or next frame if we don’t mind the added latency.

There’s also the question of code reuse. It’s very easy to reuse some low level functions, but what happens when you want to apply the same operation to a Diver and to a Fish? Since they’re not using inheritance, you can’t use polymorphism. I’ll cover that in a later blog post, but the quick preview is that you extract any common data that both structs have and work on that data in a homogeneous way.

What do you think of this approach? In which ways do you think it falls short, and in which ways do you like it better than your current style?