How to create a typed stack using Objective-C

Question

I can create a stack class quite easily, using push and pop accessor methods to an NSArray, however. I can make this generic to take any NSObject derived class, however, I want to store only a specific class in this stack.

Ideally I want to create something similar to Java's typed lists (List or List) so that I can only store that type in the stack. I can create a different class for each (ProjectStack or ItemStack), but this will lead to a more complicated file structure.

Is there a way to do this to restrict the type of class I can add to a container to a specific, configurable type?

Answer 1

You can try something like this, although I do not recommend it:

@interface TypedMutableStack : NSObject {
   Class type;
@private
   NSMutableArray *internal;
}

- (id) initWithType:(Class) type_;

@end

#define CHECK_TYPE(obj) if(![obj isKindOfClass:type]) {\
      [NSException raise:NSInvalidArgumentException format:@"Incorrect type passed to TypedMutableStack"];\
 }


@implementation TypedMutableStack

- (void) dealloc {
  [internal release];
  [super dealloc];
}

- (id) initWithType:(Class) type_ {
   self = [super init];
   if(self) {
      type = type_;
      internal = [[NSMutableArray alloc] init];
   }
   return self;
}

- (void) addObject:(id) obj {
   CHECK_TYPE(obj);
   [internal addObject:obj];
}

- (void) replaceObjectAtIndex:(NSUInteger) index withObject:(id) obj {
    CHECK_TYPE(obj);
    [internal replaceObjectAtIndex:index withObject:obj];
}

- (void) insertObject:(id) obj atIndex:(NSUInteger) index {
    CHECK_TYPE(obj);
    [internal insertObject:obj atIndex:index];
}

//...
@end