Question

Here is an example of a variadic function in Obj C.

// This method takes an object and a variable number of args
- (void) appendObjects:(id) firstObject, ...;

Is it really mandatory to have the first argument as an Obj C object? If not, what should be the syntax?

EDIT: Thanks for your responses – the first argument does not need to be an NSObject, but what I meant to ask is: Is it possible to do away with the first argument altogether? I probably did not frame the question well the first time around; sorry about that

- (void) appendObjects: ...;

The above declaration throws the following error: Expected ';' after method prototype

Answer 1

It doesn’t have to be anything really. There are two hidden arguments to every Objective-C method, self, and _cmd (in that order). self is self-explanatory (haha), but a lesser-known one is _cmd, which is simply the selector that was used to invoke the current method. This makes it possible to use variadic arguments with Objective-C methods seemingly without using an initial argument like you do with a standard variadic C function.

- (void) someMethod:...
{
    va_list va;

    va_start(va, _cmd);

    // process all args with va_arg

    va_end(va);
}

Then you can call the method like this:

 [someObj someMethod:1, 2, 3];