Question

Xcode’s dispatch_after template

double delayInSeconds = 2.0;
double delayInNanoSeconds = delayInSeconds * NSEC_PER_SEC;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInNanoSeconds);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
});

causes the following warning

Implicit conversion turns floating-point number into integer: ‘double’ to ‘int64_t’ (aka ‘long long’)

because

delayInNanoSeconds is converted from a double to an int64_t implicitly

How bad is this?

Answer 1

Once you’ve converted the time from seconds (expressed in delayInSeconds) to nanoseconds (expressed in delayInNanoSeconds), you don’t need the extra precision of a double and it’s safe to convert to a long long. You can cast it in the call to dispatch_time():

double delayInSeconds = 2.0;
double delayInNanoSeconds = delayInSeconds * NSEC_PER_SEC;

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW,
                                        (int64_t)delayInNanoSeconds);

dispatch_after(popTime, dispatch_get_main_queue(), ^(void){});

This should cause the warning to go away. Alternatively you could change the type of delayInNanoSeconds.