How can I create a static NSString[] of static NSString constants?

Question

I have a collection of static NSString consts in one of my header files that I would like to utilize in a new static NSArray (or NSString[]) but am running into the following error

Initializer Element is not a compile-time constant

My strings and array are set up as follows:

static NSString * const SOMEVAL = @"val";
static NSString * const SOMEKEY = @"key";

static NSString *KEYLIST[] = { SOMEVAL, SOMEKEY };

Is it possible to get this static array to compile in this manner or will the previously declared NSStrings always show up as non-compile-time constants?

Note that `static NSString *KEYLIST[]` is not describing an NSArray. — Hot Licks, Oct 02 '14 at 18:33

score 2 · Accepted Answer · edited May 23 '17 at 10:26

The compiler will never treat objects as "compile-time constants"; you will have to do one of two workarounds.

You can use preprocessor definitions for the strings:

#define KEY @"key"
#define VAL @"val"

static NSString * const key = KEY;
static NSString * const val = VAL;

static NSString * keyVal[] = { KEY, VAL };

Or you can initialize the array in a function or method which is guaranteed to be called before you need the array. The constructor function attribute is one option:

static NSString * keyVal[2];

__attribute__((constructor))
void setKeyVal(void)
{
    keyVal[0] = key;
    keyVal[1] = val;
}

The +initialize method of a closely-related class is another.

score 0 · Answer 2 · answered Oct 02 '14 at 19:33

You shouldn't use static in a header file. In the header declare:

extern NSString * const SOMEVAL;
extern NSString * const SOMEKEY;

extern NSString *KEYLIST[];

and then in a source file define:

NSString * const SOMEVAL = @"val";
NSString * const SOMEKEY = @"key";

NSString *KEYLIST[] = { SOMEVAL, SOMEKEY };

score 0 · Answer 3 · answered Oct 02 '14 at 19:45

0

If you're willing to rely on the compiler combining identical string constants (a pretty safe bet), you can do this instead:

#define SOMEVAL @"val"
#define SOMEKEY @"key"

static NSString *KEYLIST[] = { SOMEVAL, SOMEKEY };

answered Oct 02 '14 at 19:45

rob mayoff

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How can I create a static NSString[] of static NSString constants?

3 Answers3