Question

Can someone point me to the specific “id type documentation” ? I’ve been through the dynamic typing docs, but I want to know how to use the type id. Specifically how to check if id is null.

Answer 1

The id type is directly related to the Objective-C language itself, rather than the Cocoa/Cocoa Touch frameworks as your original tags implied. There is also no dynamic typing involved. Here’s a little introduction in Apple’s docs.

To answer your specific question, quoted from the above link:

The keyword nil is defined as a null object, an id with a value of 0. id, nil, and the other basic types of Objective-C are defined in the header file objc/objc.h.

nil and NULL are equivalent (zero pointers), and therefore interchangeable.

In a basic if statement, you just do this:

id myId = [[something alloc] init];

// Short for if (myId == nil)
if (!myId) {
    // myId is nil
} else {
    // myId is not nil
}