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Question

Method parameter that can take an object or a nil?

Answer 1

+2 A:

You can always pass nil instead of an object, there's nothing special you need to specify.

kubi 2010-05-24 20:20:42

That's hilarious. I assumed I'd have to notify obj-c in triplicate, like so many other parts of the language. No wonder I couldn't find that documented anywhere!

Dan Ray 2010-05-24 20:28:37

The constant `nil` is defined as `(id)0` — so it is an object, and thus can be passed to most methods that take objects. (Some methods disallow nil, but *that* is the exception to the rule. For example, NSArray can't contain nil, so attempting to add nil to an array will create an exception.)

Chuck 2010-05-24 21:06:25

As a side-note, that's nothing to do with the way `-addObject:` or similar is declared; the implementation simply checks whether the object passed in is `nil` and if so throws an exception. Passing `nil` as a parameter to the method is – from the language perspective – still perfectly valid.

Perspx 2010-05-24 21:35:08

Answer 2

+2 A:

- (void) myMethod:(Parameter *)aParameter {
  if (aParameter == nil) {
    ...
  } else {
    ...
  }
}

Elsewhere:

[anObject myMethod:foo];

Or:

[anObject myMethod:nil];

Dave DeLong 2010-05-24 20:21:32

Thanks, and an upvote for the code example. @kubi gets the check mark for beating you by less than a minute.

Dan Ray 2010-05-25 12:19:21

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Method parameter that can take an object or a nil?

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