title: typescript: interface for fixed size array
body: <p>Is there a way in typescript define fixed size array. say, for example, in a function definition, I need to able to say</p>
  
  <pre><code>coord: (c:any) =&gt; number[]; //how to say it is an array of size 4
  </code></pre>
  
  <p>can I define an interface like we define a hash map</p>
  
  <pre><code>//this doesn't work
  interface IArray{
    [number]
  }
  </code></pre>
  
  <p>and also restrict max length to be 4.</p>