ameter'>O2</span>&gt;(<span class='token-externalParam'>_</span> <span class='token-internalParam'>source1</span>: O1, <span class='token-externalParam'>_</span> <span class='token-internalParam'>source2</span>: O2, <span class='token-externalParam'>resultSelector</span>: <span class='token-keyword'>@escaping</span> (O1.Element, O2.Element) <span class='token-keyword'>throws</span> -&gt; Self.Element) -&gt; Observable&lt;Self.Element&gt; <span class='token-keyword'>where</span> O1 : ObservableType, O2 : Obs