LBGuard.h

#define LBGuard(cond, ...) \
  BOOL __COND_SUCCESSFUL_AT ## __LINE__ = (cond); \
  if(!__COND_SUCCESSFUL_AT ## __LINE__) {\
    NSString *failureReason = [NSString stringWithFormat:__VA_ARGS__]; \
    NSAssert(NO, @"Guard failed: %@: %@", @#cond, failureReason); \
    NSLog(@"Guard failed: %@: %@", @#cond, failureReason);\
  } \
  if(__COND_SUCCESSFUL_AT ## __LINE__) {}


// Usage:

LBGuard([fluxCapacitor isCharged]) else {
  *error = [NSError fluxError];
  return nil;
}