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    <p>Essentially, the root of the issue is a hack for wanting to return a second (optional) object.</p> <p>How can we do this, as we can only return one thing? Well, we could return some sort of <code>(return_value, error)</code> tuple, but that's a bit unwieldy. We can have as many parameters as we like though, can we do something with those...</p> <p>So, methods/functions can't modify their parameters (to be precise, they operate with a copy, so any modifications they make are local). That is to say (concurrency issues aside) the value of <code>fetchRequest</code> before the message in your question will be equal to the value of <code>fetchRequest</code> afterwards. Note the object pointed to by <code>fetchRequest</code> might change, but the value of <code>fetchRequest</code> itself won't.</p> <p>This puts us in a bit of a bind. Except, wait, we know we can happily take the value of a parameter and modify what it points to! If you look at the declaration for <code>executeFetchRequest:error:</code> you'll see it takes an <code>NSError**</code>. That's "a pointer to a pointer to an <code>NSError</code>". So, we can initialise an empty/dangling <code>NSError*</code>, find the address of it (with the <a href="http://en.wikipedia.org/wiki/Operators_in_C_and_C++#Member_and_pointer_operators" rel="noreferrer">unary <code>&amp;</code> operator</a>), and pass that in. The method can then assign to the <code>NSError*</code> pointed to by this.</p> <p>Voila, we effectively have optional additional return values.</p>
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    1. POWhy is `&` (ampersand) put in front of some method parameters?
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    1. COThanks for the explanation. I believe I ALMOST understand it. I understand a local copy of fetchRequest is made in the method in order to work so the original fetchRequest will remain unchanged. But why then does the object pointed to by fetchRequest change but the value of fetchRequest doesnt?
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    2. COTry this analogy: I tell you to "count the files in box 3 over there and tell me how many there are". I'm the caller, and I've given you a pointer. You can now do whatever you like to the contents of box 3 (modify the object at the pointer you've given), and you can even decide you're going to ignore what I told you and look at box 2, but none of that affects the value of what I gave you (the caller's context)
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    3. COmind blown! Agreed! Understood...must parse for later use!
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