objective-c determine if parameter is an object

Question

in Objective-c I have this function prototype: -(NSString*)formatSQL:(NSString*) sql, ... I may pass to this function any type of parameters: NSString, NSNumber, integer, float How can I determine in the function if a parameter is an object (NSString..) or a primitive (integer...)? thanks BrochPirate

Answer 1

If you're going to have a parameter that accepts multiple types, you can only safely do it by using Obj-C objects, which means using id as the type. You can't safely inter-mingle id with float, integer etc.

If you wrapped up all floats and ints in NSNumbers, you could have a method like so:

- (NSString *)formatSQL:(id)obj
{
    if ([obj isKindOfClass:[NSString class]]) {
        // Format as a string
    }
    else if ([obj isKindOfClass:[NSNumber class]]) {
        // Further processing will be required to differentiate between ints and floats
    }
}

There are a few caveats to using isKindOfClass:, but this should serve as a good starting point.

Answer 2

Tried this. The thing is, if the parameter (say 'obj'), is a primitive (interger, float), the command: [obj isKindOfClass:... kills the app with "bad access" error. This error is not trapable by @try/@catch - otherwise this would have been a way to identify the type. thanks though, Broch

I understand that an NSNumber wrapper would circumvent the initial propblem, however I am trying to minimize the impact on other code pieces therefore woluld appriciate a way to distinguish between 'object' an 'primitive'.

It might help if I had a way to assert whether an object (actually a pointer) points to a valid address within my address space...

Thanks Broch