Reference to generic type 'Set' requires arguments in <...> & Generic Parameter 'element' could not be inferred
<p>I was working on In-App Purchases and came across two errors. </p>

<p>The first one is <code>private let productIdentifiers: Set</code> It comes up with the error <strong>"Reference to generic type 'Set' requires arguments in &lt;...>"</strong></p>

<p>The second error in my code is <code>private var purchasedProductIdentifiers = Set()</code>  It comes up with the error <strong>"Generic parameter 'Element' could not be inferred"</strong> </p>

<p>Here is most of my code near the two errors:</p>

<pre><code>public class IAPHelper : NSObject  {

private let productIdentifiers: Set
private var purchasedProductIdentifiers = Set()

private var productsRequest: SKProductsRequest?
private var productsRequestCompletionHandler: ProductsRequestCompletionHandler?

 static let IAPHelperPurchaseNotification =     "IAPHelperPurchaseNotification"

public init(productIds: Set&lt;ProductIdentifier&gt;) {
self.productIdentifiers = productIds


super.init()
 }
}
</code></pre>

<p>Help would be nice!!</p>

<p>EDIT: I now get the error '>' is not a postfix unary operator when I change the second error to <code>private var purchasedProductIdentifiers =  Set&lt;ProductIdentifier&gt; = Set()</code></p>