I spent this last week in the Boston area, visiting a customer site. The work went well, so I'm feeling pretty good about the trip.
While I was there, I had dinner with Norm Megill (of Metamath fame). I'm really glad I finally got to meet him in person. While we have had a great correspondence solely over the Internet, there's nothing like really getting to know a person. I want to make more room in my life for this kind of thing.
Cross-platform UI design
I'm not claiming that my way is necessarily best, but for the time being I am building a separate UI for each platform, and trying to factor as much as possible into platform-independent code.
And so far it seems to be going well. It helps that (at least so far) my app is not very "UI-heavy", meaning that I don't have lots of buttons, menus, special widgets, and the like.
There's some duplication, but actually less than I expected. I deal with duplication all the time when I code. When Excessive duplication is a sign that the code needs re-factoring, and I generally find I can do that. On the other hand, if such refactoring would add more bloat with the new abstraction layer or whatever than saved by eliminating the duplication, it's maybe not such a great idea.
I also want to make a distinction between the problems of coding, which I don't mind, and problems of building and packaging, which I do. I expect that my lightweight C approach, without taking on lots of dependencies to libraries, scripting language implementations, and so on, will generate small, simple executables (or app bundles or whatever the hell platforms want) that should be generally pretty easy to build and package.
I've been thinking about these issues a bit, so...
A small rant about building and packaging
It's not hard to get a program written, compiled, and running on your own development system. It is generally harder to get that program packaged so that others can do development on it, and so that end users can get it installed correctly.
The problem gets a lot worse if you want your program to be cross-platform. Most IDE's and other development tools have a strong tendency to lock you into a specific platform. For example, I generally find using XCode pleasant, but it's not really helpful if you want to deploy those projects to other platforms. I'm sure the reasons for encouraging lock-in are more political than technical, but I also think there is a technical issue at the core.
An analogy comes to mind. Many, many programmers feel that they shouldn't have to deal with manual memory management. A good implementation of garbage collection in the runtime avoids the time investment needed to match up all the mallocs with corresponding frees, not to mention avoiding the problems that inevitably happen when the programmer gets it wrong: memory leaks, double-free and similar bugs, and, in many cases, security holes.
I actually don't feel this way strongly about memory management, at least for the type of programming I usually do. Typically, I spend so much time and effort working out the algorithms that I don't really mind the additional time needed to nail down the memory management. And, of course, since most of what I do is very performance-sensitive (2D graphics), I really appreciate the control over things like memory layout, with its strong implications on cache efficiency and so on. But if I were doing a different kind of programming (say, focussed on user interaction), I could totally understand the feeling. Why spend the time?
And I do feel that way about the build and packaging issues. Why should I have to spend a significant fraction of the time it takes me to write a program to write makefiles, config scripts, and so on? Further, why should I have to do so much more of that work if I want my program to be cross-platform, even though for the most part the algorithms should be equally valid on any platform?
To make matters worse, I consider most of the extra packaging work to be man-made, and quite ephemeral. Twenty years from now, I think there will still be runtimes with manual memory management, for which carefully crafted code is still useful (I grant that GC runtimes are likely to gain in popularity, though). However, I doubt that .pbxproj directories, MS Visual Studio Solution files, or the like will still be of much use.
Interpreted languages, or JIT bytecodes for that matter, have the potential to solve some of these packaging issues, but just being interpreted is nowhere near sufficient. I want to be able to take a source directory, press a button, and have ready-to-use packages for Linux, Win32, and Mac pop out. By "ready-to-use", I mean that the end user doesn't have to manually install prerequisite packages or libraries (as is almost invariably the case with, say, Java). In theory, it shouldn't be hard to do something like this; you just glue your source directory to a template that contains everything you need, and tar it up in whatever package format the target system expects.
When it comes down to it, though, even using an interpreted language doesn't buy you all that much. Cross-compiling C (or, for that matter, most any currently popular language) into x86 or PPC machine code is a solved problem. As far as I can see it, the only thing that's really missing is the will to actually make an infrastructure for cross-platform package building.