Specific Class type parameter in Objective-C

Question

I want to accept a Class object as a parameter to a constructor of one of my classes. It needs to do a lot of custom work with it, and I want to abstract that away from the use

Answer 1

Not at compile-time, but you can release self and return nil if the class is invalid:

- (id)initWithCar: (Class)carClass {
    self = [super init];

    if (self) {
        if (![carClass isSubclassOfClass:[Car class]]) {
            [self release];
            self = nil;
        } else {
            // Normal initialization here.
        }
    }

    return self;
}

That's the closest you'll get to the sort of restriction you want.

But this sort of design suggests you need to rethink your class hierarchy. Rather than passing a subclass of Car, you should have a Manufacturer class. Something like this:

@interface Manufacturer : NSObject
+ (id)manufacturerWithName: (NSString *)name;

- (NSArray *)allCars;
@property (readonly) Car *bestsellingCar;
// etc.
@end

#define kManufacturerVolvo [Manufacturer manufacturerWithName: @"Volvo"]
#define kManufacturerToyota [Manufacturer manufacturerWithName: @"Toyota"]
// etc.

And then this initializer for Dealership:

- (id)initWithManufacturer: (Manufacturer *)aManufacturer;