Question

If I have an object myObject of class id, how would I “cast” it as a CGPoint (given that I have performed introspection and know myObject to a CGPoint)? This is despite the fact that CGPoint is not a real Obj-C class.

Simply doing (CGPoint)myObject returns the following error:

Used type 'CGPoint' (aka 'struct CGPoint') where arithmetic or pointer type is required

I want to do this so that I can check if the object being passed to an NSMutableArray is a CGPoint, and if it is, to wrap the CGPoint in an NSValue automatically; e.g.:

- (void)addObjectToNewMutableArray:(id)object
{
    NSMutableArray *myArray = [[NSMutableArray alloc] init];
    id objectToAdd = object;
    if ([object isKindOfClass:[CGPoint class]]) // pseudo-code, doesn't work
    {
        objectToAdd = [NSValue valueWithCGPoint:object];
    }
    [myArray addObject:objectToAdd];
    return myArray;
}

ADDITIONAL CODE

Here are the functions I use to perform “introspection”:

+ (BOOL)validateObject:(id)object
{
    if (object)
    {
        if ([object isKindOfClass:[NSValue class]])
        {
            NSValue *value = (NSValue *)object;
            if (CGPointEqualToPoint([value CGPointValue], [value CGPointValue]))
            {
                return YES;
            }
            else
            {
                NSLog(@"[TEST] Invalid object: object is not CGPoint");
                return NO;
            }
        }
        else
        {
            NSLog(@"[TEST] Invalid object: class not allowed (%@)", [object class]);
            return NO;
        }
    }
    return YES;
}

+ (BOOL)validateArray:(NSArray *)array
{
    for (id object in array)
    {
        if (object)
        {
            if ([object isKindOfClass:[NSValue class]])
            {
                NSValue *value = (NSValue *)object;
                if (!(CGPointEqualToPoint([value CGPointValue], [value CGPointValue])))
                {
                    NSLog(@"[TEST] Invalid object: object is not CGPoint");
                    return NO;
                }
            }
            else
            {
                NSLog(@"[TEST] Invalid object: class not allowed (%@)", [object class]);
                return NO;
            }
        }
    }
    return YES;
}

+ (NSValue *)convertObject:(CGPoint)object
{
    return [NSValue valueWithCGPoint:object];
}

Answer 1

A CGPoint is not an Objective-C object. You cannot pass one to your addObjectToNewMutableArray: method. The compiler will not let you.

You need to wrap the CGPoint in an NSValue and pass that wrapper to your addObjectToNewMutableArray: method.

If you have an NSValue and you want to test whether it contains a CGPoint, you can ask it like this:

if (strcmp([value objCType], @encode(CGPoint)) == 0) {
    CGPoint point = [value CGPointValue];
    ...
}