Objective C: how to compare primitive types with objects

Question

I'm trying to write a method that compares 2 objects. The problem I have is: how do I know if a property of a primitive type?

+(BOOL)isObject:(void*)object1 equalTo:(void*)object2
{
if (object1 == nil && object2 == nil)
    return TRUE;

if ((object1 != nil && object2 == nil) ||
    (object1 == nil && object2 != nil) || 
    ([object1 class] != [object2 class]))
    return FALSE;

if (object1 != object2)
{
    u_int count;
    Ivar* ivars = class_copyIvarList([object1 class], &count);
    for (int i=0; i < count; i++)
    {
        id v1 = object_getIvar(object1, ivars[i]);
        id v2 = object_getIvar(object2, ivars[i]);
        if (![ObjectComparer isObject:v1 equalTo:v2])
            return FALSE;
    }
}
return TRUE;    
} 

That will work for objects but fail for primitive types. Another thing is I want to pass parameters as something general such as id but does not work for primitives. At least i need to know that it is a primitive type and convert it into id.

Any ideas?

Answer 1

Answering strictly on properties (as in class_copyPropertyList), not on instance variables (as per your current code's class_copyIvarList)...

People usually dodge around the issue by using key-value coding. If you use valueForKey: then the runtime automatically promotes primitives to object types.

If you were to implement that at the Objective-C level you'd get the NSMethodSignature using -methodSignatureForSelector: and check the methodReturnType property, which is in the standard Objective-C type encoding form (ie, to match @encode).

Working directly with the C runtime, I imagine you'd use method_copyReturnType on the getter.

As for instance variables, I'm not sure there's a way to query their type.

Note also that the normal way of handling this is to have objects themselves implement isEqual:. It's part of NSObject so guaranteed always to be defined. Classes themselves should implement the logic they need to perform comparison by value.