How to create constant NSString by concatenating strings in Obj-C?

Question

I\'m trying to instanciate a constant NSString by concatanating other NSString instances.

Here is what I\'m doing in my implementation file :

static          


        

Answer 1

I think you need to step back and think about if the string needs to be defined as a const.

Clearly the string isn't a constant since you are trying to assign a new value to it - and that is not possible since you specifically instructed the compiler to make sure the value wasn't changed by using the const keyword.

If the string resides as a property in a class you could make it a read-only property - i.e. accessor method but no setter method. You would then be able to construct your string as you wish in the class internally while keeping the callers from changing the value.

Answer 2

I thought there must be a way to do this but the best I could do was using a #define directive. For example,

// Define the base url as an NSString
#define BASE_URL @"http://www.milhouse.co.uk/"

// Now the derived strings glued by magic
NSString *const kBaseURL    = BASE_URL;
NSString *const kStatusURL  = BASE_URL @"status.html";
NSString *const kBalanceURL = BASE_URL @"balance.html";

Answer 3

static const objects value is determined at compile-time so you indeed cannot add any method calls to their initialization. As an alternative you can do the following:

static NSString *const MY_CONST = @"TEST";
static NSString *MY_CONCATENATE_CONST = nil;

if (nil == MY_CONCATENATE_CONST)
   MY_CONCATENATE_CONST = [NSString stringWithFormat:@"STRING %@", MY_CONST];