title: Combine: Convert Closure into Publisher
body: <p>How to convert:</p>
  
  <pre><code>func getResults(completion: ([Result]?, Error) -&gt; Void)
  </code></pre>
  
  <p>Into</p>
  
  <pre><code>var resultsPublisher: AnyPublisher&lt;[Result], Error&gt;
  </code></pre>
  
  <p>Just a scheme how I see it is (this syntax doesn't exist):</p>
  
  <pre><code>var resultsPublisher: AnyPublisher&lt;[Result], Error&gt; {
    let publisher: AnyPublisher = ... // init
    getResults { results, error in
       guard let results = results else {
         publisher.produce(error: error) // this syntax doesn't exist
         return
       }
  
       publisher.produce(results: results)  // this syntax doesn't exist
  
    }
  
    return publisher
  }
  </code></pre>
  
  <p>I need that because some 3d party SDKs use <code>completion closures</code> and I want to write extensions to them that return <code>Publishers</code>.</p>