title: Is it possible to reuse type parameter of generics of some class
body: <p>For example I have following code </p>
  
  <pre><code>    class Foo {
        bar: Promise&lt;string[]&gt;;
  
        // a is the same type as type of promise in bar 
        baz(a: ????): Foo['bar'] {
          // some code
          return Promise.resolve(a);
        } 
      }
  </code></pre>
  
  <p>I can get type of bar - but I would like to get the type inside promise without creating extra type or interface.</p>
  
  <p>I've searched a lot and I think this is not implemented or suggested yet, but before creating feature request I want to be sure.</p>