Swift 3.0 conversion - contains(_:) in Collection
<p>I am trying to convert a project from Swift 2.3 to Swift 3.</p>

<p>Here is some issue with <code>contains(_:)</code> from <code>Collection</code>:</p>

<pre><code>extension Collection {
    subscript (safe index: Index) -&gt; Iterator.Element? {
        return indices.contains(index) ? self[index] : nil
    }
}
</code></pre>

<p>The error is <code>Missing argument label 'where:' in call</code></p>

<p>I added <code>where:</code>, but now, another error appears:</p>

<p><code>Cannot convert value of type 'Self.Index' to expected argument type '(_) throws -&gt; Bool'</code></p>

<p>From Swift 3.0 language guide it seems that it should work without errors:</p>

<pre><code>if favoriteGenres.contains("Funk") {
    print("I get up on the good foot.")
} else {
    print("It's too funky in here.")
}
</code></pre>