Class1

- (void)printDummyStuff
{
    TestClass1 *tc1 = [[TestClass1 alloc] init];
    [tc1 performSimulationWithFitnessFunction:^ int (int a)
     {
         int b = [self stuff:a];
         int c = [self magic];
         return b * (c + b * c);
     }];
}

- (void)print:(NSString *)number
{
    NSLog(@"Print dummy stuff! %@", number);
}

Class2

- (void)performSimulationWithFitnessFunction:(int(^)(int))f
{
    [self setFitnessFunction:f];
    [object performSimulationWithFitnessFunction:f];
}