Question

FMParallaxChild.h

typedef struct {
    // ...
} FMParallaxSetting;

inline extern FMParallaxSetting FMParallaxSettingMake(CGPoint ratio, CGPoint startPos, CGPoint offset, CGPoint relVel, int zOrder);
inline extern FMParallaxSetting FMParallaxSettingMake(CGPoint ratio, CGPoint startPos, CGPoint offset, CGPoint relVel, int zOrder) {
    // ...
}

FMParallax.h

#import "FMParallaxChild.h"
....

MyController.h

#import "FMParallax.h"
....

AppDelegate.m

#import "MyController.h"
....

From this simplified setup I am getting a duplicate symbol linker error:

ld: duplicate symbol _FMParallaxSettingMake in MyController.o and AppDelegate.o

I can’t find any import loops and I only import FMParallaxChild.h in a single place, so what am I doing wrong?

Answer 1

Declare it as static inline for c or objc:

static inline FMParallaxSetting
  FMParallaxSettingMake(CGPoint ratio,
                        CGPoint startPos,
                        CGPoint offset,
                        CGPoint relVel,
                        int zOrder) {
  // ...
}

or just inline for c++ or objc++:

inline FMParallaxSetting
  FMParallaxSettingMake(CGPoint ratio,
                        CGPoint startPos,
                        CGPoint offset,
                        CGPoint relVel,
                        int zOrder) {
  // ...
}

of course, with c++ and objc++, your program will fall back on the One Definition Rule in this case (which is a good default).

The problem as it is, is that it will be exported for each translation it is visible (#included) in.