Function Templates in Objective-C

If you're lucky enough to experience my TwitStream lately, then you might have noticed that I've been doing some iPhone development. That means I'm working in Objective-C. It's reflection capabilities are interesting, to say the least. Low overhead reflection does allow for some code templates. Take a look at this.

double MeanTime(SEL selector){
 NSArray *dataList = GetDataList();
 if ([dataList count] == 0){
  return 0.0;
 }
 double cnt = (double) [dataList count];
 double sum = 0.0;
 for (StatData *data in dataList){
  if ([data respondsToSelector:selector]){
   sum += [[data performSelector: selector] doubleValue];
  }
 }
 return sum/cnt; 
}
double MeanDownloadTime(void){
 return MeanTime(@selector(downloadTime));
}
double MeanProcessingTime(void){
 return MeanTime(@selector(processingTime));
}
double MeanTotalTime(void){
 return MeanTime(@selector(totalTime));
} 

Yeah, I know, what's up with the C-style functions? This was inherited code where I was only changing the implementation of those functions, and I didn't feel like wrapping them in a nice pretty class just for the blog. The StatData class has several synthesized properties, including downloadTime, processingTime, and totalTime. I needed three functions that iterated over a list of StatData and computed the average of these properties. Objective-C's selectors provided a nice way to do this. I have to admit that I tried to over-think this at first, and tried using @selector(getDownloadTime:) at first, instead of @selector(downloadTime). I thought that this would be the method name that the compiler would synthesize from the property. This didn't even work, but the more obvious, straightforward usage did.