-[NSInvocation getReturnValue:] with double value produces 0 unexpectedly

Question

I am trying to call a method that returns a double using NSInvocation. But I found that it does not working in 64 bit iOS apps. It works on on OS X, in

Answer 1

Fix based on @TomSwift answer.

    - (void)testInvocation
    {
        NSInvocation *invocation = [[self class] invocationWithObject:self selector:@selector(getAFloat)];

        [invocation setTarget:self];
        [invocation invoke];

        double d;
        [invocation getReturnValue: &d];
        NSLog(@"d == %f", d);

        return YES;
    }

    + (NSInvocation *)invocationWithObject:(id)object selector:(SEL)selector
    {
        NSMethodSignature *sig = [object methodSignatureForSelector:selector];
        if (!sig) {
            return nil;
        }

    #ifdef __LP64__
        BOOL isReturnDouble = (strcmp([sig methodReturnType], "d") == 0);
        BOOL isReturnFloat = (strcmp([sig methodReturnType], "f") == 0);

        if (isReturnDouble || isReturnFloat) {
            typedef struct {double d;} doubleStruct;
            typedef struct {float f;} floatStruct;

            NSMutableString *types = [NSMutableString stringWithFormat:@"%s@:", isReturnDouble ? @encode(doubleStruct) : @encode(floatStruct)];
            for (int i = 2; i < sig.numberOfArguments; i++) {
                const char *argType = [sig getArgumentTypeAtIndex:i];
                [types appendFormat:@"%s", argType];
            }

            sig = [NSMethodSignature signatureWithObjCTypes:[types UTF8String]];
        }
    #endif

        NSInvocation *inv = [NSInvocation invocationWithMethodSignature:sig];
        [inv setSelector:selector];
        return inv;
    }