Swift: index(of:) doesn't exist? : <p>I keep trying to use index(of:) on Array objects but it doesn't come up in the autocomplete (or whatever that menu is called) and, of course, doesn't build. I see it right there in the documentation! It's there! I want it! What's going on here?</p>

<p>(Btw this isn't the only Array method I can't access. For just one example, I can't use suffix(from:), I can only use suffix(maxLength:), plus it's implemented as suffix(_ maxLength:) even though the documentation lists it as requiring an argument name)</p>
