Question

I need a string->string mapping to be used at runtime (think NSDictionary), except the mapping will NEVER change after build-time.

The naive solution is to just use an NSDictionary, but there has to be a more optimal way to do this, no?

Optimal in the sense that if the mapping is known at compile-time, and known to never change, the compiler should be able to do the mapping at compile-time. An NSDictionary needs to do a hash lookup at runtime. I know it’s constant time, but it just feels a bit “unclean” to me…

Answer 1

A static NSDictionary is the right tool for this. You typically initialize these with an +initialize method:

static NSDictionary *kDictionary;

+ (void)initialize {
  if (self == [MYClass class]) {
    kDictionary = [[NSDictionary alloc] initWith...];
  }
}

initialize is called one time per class, with thread safety, immediately before the first requested method is called on that class (usually this first method is +alloc). The self test is because subclasses will automatically call their [super initialize], and you generally don’t want to run this more than once in that case.