#include <Availability.h>
#include <TargetConditionals.h>
#if TARGET_OS_OSX
# if __MAC_OS_X_VERSION_MIN_REQUIRED != __MAC_10_11
# error macOS deployment version mismatch
# endif
#elif TARGET_OS_IOS
# if __IPHONE_OS_VERSION_MIN_REQUIRED != __IPHONE_9_1
# error iOS deployment version mismatch
# endif
#elif TARGET_OS_WATCH
# if __WATCH_OS_VERSION_MIN_REQUIRED != __WATCHOS_2_0
# error watchOS deployment version mismatch
# endif
#elif TARGET_OS_TV
# if __TV_OS_VERSION_MIN_REQUIRED != __TVOS_9_0
# error tvOS deployment version mismatch
# endif
#else
# error unknown OS
#endif
void foo()
{
}