Not allowing to use Constant defined in Objective

Question

I created Objective C Header file. and added some properties in it.
i declared
static NSString* const kColor005C98 = @"005C98"; in Constants.h file

I defined this file in Bridging-Header file as #import "Constants.h" Now when i want to use this property kColor005C98 in some swift file it failed the build and i am getting

Undefined symbols for architecture armv7: "_kColor005C98", referenced from:

i don't know what else i need to do so i don't get this error? (i have used this property in other objective C file successfully and no issue in that case)

Answer 1

Update:

As of Swift 2/Xcode 7 and later, a static constant definition like

static NSString* const kColor005C98 = @"005C98"; // in Constants.h file

is imported to Swift and can be used without problems.

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(Old answer for Swift 1.x) When the code

static NSString* const kColor005C98 = @"005C98"; // in Constants.h file

is processed by an Objective-C compiler, it is treated as two things combined into one statement:

• A variable declaration which introduces an identifier and describes its type, and
• a variable definition which actually instantiates/implements this identifier.

See for example What is the difference between a definition and a declaration? for a good explanation of the difference between declaration and definition.

The Swift compiler treats the statement only as a declaration. Therefore the variable is not defined anywhere, causing the linker error.

To solve the problem, you have to move the definition to an Objective-C file:

// Constants.m:
#import "Constants.h"
NSString * const kColor005C98  = @"005C98";

and change the declaration to an extern declaration:

// Constants.h:
extern NSString * const kColor005C98;

Alternatively, you can just remove the static modifier:

 NSString * const kColor005C98 = @"005C98";

to make it work with Swift. The disadvantage is that when this line is included by multiple Objective-C files, all of them will define a globally visible symbol kColor005C98, causing "duplicate symbol" linker errors.

Another alternative is to use a macro definition instead:

#define kColor005C98 @"005C98"