I have always strong recommended segregating Objective-C and C++ code with a thin Objective-C++ wrapper. I do not like Objective-C++. It is useful for what it does, but it is a mess of a “language.” It has many downsides, for slower compiles and poor debugging facilities, to confusing code and inefficient ARC code. .mm is a blight on your code. Never let it spread.

That said, Objective-C++ is invaluable for integrating C++ into Objective-C. And while I am not a great lover of C++, it is a very useful language and there is a great deal of excellent code written in it that is well-worth reusing in your Cocoa projects. Many of Apple’s frameworks are implemented in C++.

So my recommendation for those who have existing C++ logic code has always been thus: write your UI in pure Objective-C (.m). Write your “middleware” in pure C++ (.cpp). And have a thin Objective-C++ (.mm) wrapper layer to glue them together. Your ObjC++ API should ideally exactly match your C++ API, just converting types (for instance converting std::string to and from NSString).

I’ve been looking into better ways to host my repositories for clients, manage task lists, documents, etc. I like github. It’s a good interface. It works. I could use a few more features in the Issues module, but it’s nice that they keep it simple. I’ve tried BitBucket and Assembla, and looked at several others. I’ve managed my own servers. In every test, github wins.

Except for price. github is often the most expensive. Especially if you need what I need, which is several small repositories, each with a small number of collaborators (often just one or two). But just a few of those can push you into the Medium plan, or even into the Bronze plan.

Thanks to @codinghorror, I recently read a blog post from Steve McConnell called 10x Productivity Myths: Where’s the 10x Difference in Compensation? Steve quotes a question from Pete McBreen:

"One point in his article that McConnell did not address--programmer compensation does not vary accordingly. This is a telling point--if the difference is productivity can be 10X, why is it that salaries rarely fall outside the 2X range for experienced developers?" [emphasis in original]

He then provides some fairly satisfying answers. “The other guy is actually overpaid.” “You’re confusing coding with actual business value.” “Companies pay the least they can get away with.” etc. All his answers make good, intuitive sense. Unfortunately, despite being a longtime fan of Steve McConnell’s work, I believe most are irrelevant or incorrect.

Last night’s CocoaHeads was a blast. Alondo, you have to come give an intermediate/advanced talk on Storyboards. Thanks a lot to @scottpenrose for his lightning and thunder, and @flightblog for his inspiration (METAR gave me a lot of headaches, too). And of course, thanks especially to Josh for organizing everything. And a new place for NSCoder? You rock.

For those who didn’t scribble notes fast enough, my Core Foundation presentation is attached (including the fix for my memory leak; was it Jay who found that?) I’ll make sure to fix the code in the book for the next edition.

Building a Core Foundation Presentation

When last we looked at Bézier curve calculations, we were able to calculate five million points in about 0.6s (~8.3Mp/s or megapoints-per-second). That’s 1000 points per curve, 100 curves, at 50fps. That was 5x faster than the original -Os optimized function. But we’re just getting warmed up. We haven’t yet gotten half of the performance available.

[If you want the answer to last time’s homework, skip to the end.]

So you want to hand-calculate Bézier curves. Good for you. It comes up more often then you’d think on iOS, even though UIBezierPath is supposed to do it all for you. The truth is, sometimes you need the numbers yourself. For instance if you want to calculate intersections, or you want to draw text along the curve (like in CurvyText from iOS:PTL chapter 18).

Chapter 18 of iOS:PTL includes code for calculating points on a Bézier curve (see CurvyText in the sample code). In the book, I hinted that this operation would likely be well suited to the Accelerate framework. The Accelerate framework provides hardware-accelerated vector operations. Solving Bézier equations seems a perfect fit. I’ll get more into Accelerate in later posts (including some thoughts on when to use it), but first I need to introduce some mathematical groundwork.

In this post, I’m targeting a specific kind of developer; one like myself. My mathematically inclined friends will find this so trivial that it’s hardly worth discussing. For those of you who have never seen a matrix before, this may be a bit dense. But if you’re like me, and once upon a time you actually took linear algebra, but today you wouldn’t know a transpose if it invited you to dinner, this may help. (The last time I computed a dot-product, the Newton hadn’t been released…) My goal isn’t to teach you Guassian elimination or eigenvalues. My goal is to show you by example the specific tools you need to convert the math you find in a book into matrices so you can calculate it faster. (And how to cheat with the incredible new tools available to us.)

The most up-to-date source for this is now available at github.

Your programs need to deal gracefully with being offline. Mugunth Kumar has built an excellent toolkit that manages REST connections while offline called MKNetworkKit, and Chapter 17 of our book is devoted to the ins-and-outs of this subject.

But sometimes you just have a simple UIWebView, and you want to cache the last version of the page. You’d think that NSURLCache would handle this for you, but it’s much more complicated than that. NSURLCache doesn’t cache everything you’d think it would. Sometimes this is because of Apple’s decisions in order to save space. Just as often, however, it’s because the HTTP caching rules explicitly prevent caching a particular resource.

What I wanted was a simple mechanism for the following case:

• You have a UIWebView that points to a website with embedded images
• When you’re online, you want the normal caching algorithms (nothing fancy)
• When you’re offline, you want to show the last version of the page

My test case was simple: a webview that loads cnn.com (a nice complicated webpage with lots of images). Run it once. Quit. Turn off the network. Run it again. CNN should display.

For those who have asked (and it’s the #1 question I’m asked about the book), iOS 5 Programming Pushing the Limits is now available in Kindle format, along with iBook and Adobe eBook. Enjoy

For those who have asked, the Adobe E-Book version of iOS 5 Programming is available now from Wiley. I’m not certain yet when the Kindle version will be out, but I’m looking into it, along with getting a list of what other formats are planned.